Racing and crowded thoughts in mood disorders: A data-oriented theoretical reappraisal Gilles Bertschy, Sebastien Weibel, Anne Giersch, Luisa Weiner

To cite this version:

Gilles Bertschy, Sebastien Weibel, Anne Giersch, Luisa Weiner. Racing and crowded thoughts in mood disorders: A data-oriented theoretical reappraisal. L’Encéphale, Elsevier Masson, 2020, 46 (3), pp.202-208. ￿10.1016/j.encep.2020.01.007￿. ￿hal-02935003￿

HAL Id: hal-02935003 https://hal.archives-ouvertes.fr/hal-02935003 Submitted on 15 Sep 2020

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Review of the literature

Racing and crowded thoughts in mood disorders: A data-oriented theoretical reappraisal

Tachypsychie dans les troubles de l’humeur : une réévaluation théorique basée sur les données de la littérature

a,b,c, a,b b a,d,e G. Bertschy ∗ , S. Weibel , A. Giersch , L. Weiner

a Pôle de psychiatrie, santé mentale & addictologie des hôpitaux universitaires de Strasbourg, 67000 Strasbourg, France b Inserm U1114, 67000 Strasbourg, France c Fédération de médecine translationnelle de Strasbourg, université de Strasbourg, 67000 Strasbourg, France d Laboratoire de psychologie des cognitions, 67000 Strasbourg, France e Faculté de psychologie, université de Strasbourg, 67000 Strasbourg, France

a r t i c l e i n f o a b s t r a c t

Article history: Objectives. – Speed of thought is a central phenomenon in mood disorders. We aimed to provide an update Received 5 October 2019 on the topic ten years after a first narrative review published on racing and crowded thoughts in mood Accepted 23 January 2020 disorders. This update is based on recent publications, including recent works of our group. Available online 6 March 2020 Methods. – Narrative review based on publications from the last ten years including publications of our group and a systematic research of references on PubMed. Keywords: Racing Results. – The traditional dichotomist view of racing versus crowded thoughts is not refuted but appears to thoughts Crowded be more complex, as revealed by validation studies of the Racing and Crowded Thoughts Questionnaire. thoughts Bipolar Moreover, this dualistic view can no longer be conceptualized in a simple bijective concordance with Depression Mood disorders the distinction of hypomania versus mixed depression. We also show that racing/crowded thoughts are strongly associated with mixed depression and not with non-mixed depression, that they tend to be more associated in hypomania to irritability than to the typical symptoms of energy and activity increase and that they are clearly distinguishable from ruminations. Yet, although tightly linked to mood disorders, racing/crowded thoughts appear to be associated to anxiety as well as attention deficit/hyperactivity disorder and insomnia. Conclusions. – Racing and crowded thoughts should be studied in a dimensional perspective as an impor- tant facet of mind activity within and beyond the field of mood disorders. .

r é s u m é

Mots clés : Objectifs. – Dix ans plus tôt a été publiée, sous la direction du premier auteur de cet article, une réévaluation Pensées accélérées théorique sur les pensées accélérées (« racing ») et grouillantes (« crowded ») dans les troubles de l’humeur, Pensées grouillantes que la tradition franc¸ aise rassemble volontiers sous le concept de tachypsychie, mais que les auteurs Tachypsychie anglo-saxons utilisent peu. Cette revue incluait des considérations théoriques sur le concept. Après une Bipolaire décade, qui a été marquée par l’émergence du concept de dépression mixte, nous proposons une mise à Dépression jour, basée sur les publications récentes incluant des travaux récents de notre groupe. Troubles de l’humeur Méthode. – Cette revue narrative s’appuie sur la réévaluation théorique initiale publiée en 2010 et reprend les publications de ces dix dernières années. Les études pertinentes ont été collectées au fil des travaux de notre groupe, incluent des publications de notre groupe et ont été complétées par une recherche systématique sur PubMed.

∗ Corresponding author at: Hôpital civil, clinique de psychiatrie, 1, place de l’Hôpital, BP 426, 67091 Strasbourg, France. E-mail address: [email protected] (G. Bertschy).

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Résultats. – Nous confirmons les éléments connus sur la tachypsychie en les étendant et en apportant cer- taines clarifications. La conception dichotomique des pensées accélérées versus les pensées grouillantes n’est pas réfutée mais elle apparaît plus complexe, comme l’a révélé les études de validation du Racing and Crowded Thoughts Questionnaire (le questionnaire de pensées accélérées et grouillantes), réalisées chez des sujets de la population générale et chez des patients bipolaires. Ces études montrent, à travers l’analyse factorielle des items composant cet auto-questionnaire, l’existence non pas de deux mais de trois facteurs. Un premier facteur décrit la suractivité des pensées, est associé à l’hypomanie et renvoie assez bien au concept de pensées accélérées linéaires, alors qu’un second facteur décrit le caractère pénible de la suractivité des pensées, est associé à l’humeur dépressive et renvoie, lui, assez bien au concept de pensées grouillantes. Il existe, cependant, un troisième facteur décrivant la surexcitabilité des pensées qui est à la fois associée à l’hypomanie et la dépression et qui vient donc brouiller les cartes du schéma dichotomique. De plus, cette vision dichotomique ne peut plus être conc¸ ue comme dans une simple concordance bijective avec la distinction hypomanie versus dépression mixte telle qu’elle était décrite dans le modèle proposé il y a dix ans. Il semble raisonnable de considérer que, dans la manie sévère, la tachypsychie n’est plus linéaire mais devient grouillante parce qu’à un certain stade, l’accélération excessive des pensées submerge les capacités de traitement de ces pensées par l’esprit. Par ailleurs, les études de la tachypsychie chez des patients déprimés, montrent que celle-ci est fortement associée à la dépression mixte et non à la dépression non mixte. Des études, sur sa présence au cours d’épisodes hypomanes, montrent que la tachypsychie tend à être plus associée à l’irritabilité qu’aux symptômes maniaques classiques d’augmentation de l’énergie et de l’activité. Ces résultats confortent l’intuition de Kraepelin et Weygandt d’un modèle à trois volets des symptômes cliniques des troubles de l’humeur dans lequel pensée associative et activité psychomotrice constituent deux volets distincts (en plus du troisième volet qui concerne les affects). Les travaux récents ont permis aussi d’apporter des éléments empiriques pour étayer la distinction entre tachypsychie et ruminations. Enfin, bien qu’étroitement liée aux troubles de l’humeur, la tachypsychie semble être associée à l’anxiété aussi bien dans la population générale que chez les sujets bipolaires. Elle est également très présente chez les sujets présentant un trouble déficit de l’attention/hyperactivité ou souffrant d’insomnie. Conclusion. – La tachypsychie, telle qu’elle s’exprime par des pensées accélérées et grouillantes, représente un concept clinique qui permet d’étudier une importante facette de l’activité de l’esprit dans une perspec- tive dimensionnelle dans et au-delà du domaine des troubles de l’humeur. .

1. Introduction can be articulated”, “This experience resembles watching two or three television programs simultaneously.” The flight of ideas is Racing thoughts refer to a subjective acceleration and overpro- described by a logorrhea (which is also considered by itself in the duction of thoughts, which have been essentially associated with criterion B3), with abrupt changing of topics, such that the speech manic episodes in bipolar disorder. Indeed, racing thoughts, and can be disorganized and incoherent. The ICD-10, the WHO classi- their verbal equivalent, flight of ideas, are extremely characteristic, fication published in1994 [9], considers only the flight of ideas in if not pathognomonic, of manic thinking [1]. As Jamison so vividly the manic episode with psychotic symptoms. described it [2], manic thought is characterized by “[. . .] a torrent of Although racing thoughts have been abundantly described by near unstoppable speech; thoughts bracchiate from topic to topic, psychiatrists, it is still unknown whether they belong to a sin- held only by a thin thread of discernible association. Ideas fly out, gle entity, or are rather a multi-faceted phenomenon. The clinical and as they do, they rhyme, pun, and assemble in unexampled ways. boundaries and characteristics of racing thoughts have not been The mind is alive, electric.” In his groundwork textbook on bipolar thoroughly evaluated in patients with mood disorders. There are disorder, Kraepelin [3] was the first to use the term “flight of ideas”, reasons to believe that racing thoughts might be associated not only to refer interchangeably to both the experience of speeded thought with full-blown manic, but also with depressive episodes in bipolar pressure, and its expression in the patient’s speech. Kraepelin con- disorder. As mentioned above, Kraepelin [3] had already suggested ception of racing thought was strongly linked to his conception that depression “with flight of ideas” and other mixed typolo- of mixed state he developed with his student Weygandt [4]. They gies of depression were common occurrences of mood episodes in described three distinct areas of psychic functioning: affect, psy- manic-depressive illness. However, when racing thoughts co-occur chomotor activity and associative thinking that could be excited with depressive mood, instead of conveying a sense of speed and or depressed, independently from the others. This resulted into flow, associated with pleasant emotions, thoughts are described eight combinations, including six mixed states (in addition to the as numerous and “overcrowded” in the patient’s head, and are two states of either homogenous excitation/mania or homoge- associated with unpleasant emotions [10–12]. Thus, phenomeno- nous depression). Among them, two mixed states combined excited logically speaking, although the term “racing thoughts” reflect an associative thinking and depressed affect. unitary concept, racing thoughts might consist of at least two The term “racing thoughts” appeared in the American classifica- kinds of thought activity – “racing” and “crowded”, associated with tion of the Diagnostic and Statistical Manual for Mental Disorders manic and depressed mood, respectively. For instance, Benazzi [12] third edition in 1980 [5], but only in the criterion B3 of mania: described crowded thoughts as “continuous flooding of the mind “flight of ideas or subjective experience that thoughts are rac- by ideas that the person could not stop” and racing thoughts as ing”. Since then, the wording has stayed the same. It became the “increased speed of thinking”. criterion B4 in the DSM-III-R [6], and in the DSM-IV [7]. The Text- In 2010, a theoretical reappraisal of the phenomenology of rac- revision version of DSM-IV [8] gives a more specific description: ing and crowded thought in mood disorders [13] was published “The individual’s thoughts may race, often at a rate faster than under the direction of one of us (GB). We propose here, a decade

later, an update on this narrative review based on new empirical these qualitative findings suggested that racing thoughts was a data that has called into question the dichotomist view of racing multi-faceted concept [19]. To address the multi-faceted nature of vs. crowded thoughts found in hypomania and mixed depression, racing and crowded thoughts which were not targeted by this early respectively. To do so, we will follow the plan of the initial theoret- scale [19], our group developed a 34-item self-rating scale, the Rac- ical review (for convenience sake we will call it the 2010 review). ing and Crowded Thoughts Questionnaire (RCTQ) assessing thought For each section, we will do a short synthesis of the 2010 review overactivity during the past 24 hour. Some of its items were related and then integrate the contribution of studies published since then, to the phenomenology of racing thoughts and refers to increased including the contributions of our group. References have been col- thought velocity [e.g. “My thoughts race much too fast”), sequential lected downstream during the 10 last years of research activity and easy unfolding (e.g. “There is a succession of thoughts in my of our group and they have been completed by a prospection on mind, racing from one to the other with incredible ease”). Some Pubmed database using the following query: (“racing”[All Fields] or items were related to the phenomenology of crowded thoughts “crowded”[All Fields]) and (“thought”[All Fields] or “thoughts”[All referring to an increased amount of simultaneous thoughts (e.g. Fields])). “I have too many thoughts at the same time”). Others were related to the negative consequences of thought overactivation (e.g. “My brain cannot manage all these thoughts that arise at the same time” 2. Evolution of the concept and of the phenomenological or “My mental overactivity is exhausting”). Items were rated on perspectives Likert scale ranging from zero (“not at all”) to four (“completely agree”). We first investigated its psychometric properties in healthy The introduction section of this paper summarized the evolu- subjects [20]. Indeed, recent studies in healthy individuals have tion of the concept until 2010. Since the 2010 review [13], the fifth reported racing thoughts in the unaffected offspring of patients edition of the DSM was published in 2013 [14]. However, it did not with bipolar disorder [21], have suggested that racing thoughts modify the wording of the B4 criterion for mania used in the preced- might be present in healthy undergraduate students [22] and young ing version (“Flight of ideas or subjective experience that thoughts adults reported their thoughts as more racing than older adults [23]. are racing.”). An important evolution is that the DSM-5 [14] fully Exploratory factor analysis of the RCTQ in healthy individuals [20] acknowledges that racing thoughts could be associated to a depres- yielded a three-factor solution, labeled “thought overactivation”, sive syndrome, coining the term “depression with mixed features” “burden of thought overactivation”, and “thought overexcitability”. to refer to the co-occurrence of subsyndromal manic symptoms in The “thought overactivation” subscale was selectively associated depressive episodes. This is a real advance even if the stringent cri- with current elated mood and included items conveying both the teria exposes to a high risk of underdiagnosis of mixed depression notion of increased amount and velocity of thoughts which echoed [15]. The ICD-11, the new version of the WHO classification pub- the concept of racing thoughts in hypomania, whereas the “burden lished online in 2018 [16], has included rapid and racing thoughts of thought overactivation” subscale was associated with current in its description of hypomanic episodes whereas flight of ideas is low mood and its content echoed the concept of crowded thoughts. associated to the description of a manic episode even in the absence The “thought overexcitability” subscale included items conveying of psychotic symptoms. The universality of racing thoughts as a the notion of distractibility, and, in contrast with the first two fac- symptom of mania has been recently illustrated in a paper about the tors, was associated with both elated and low mood. Subsequently, concept of mania in traditional Andean culture [17]. Noteworthy is in a large clinical study including French, Italian and Belgian bipo- also the publication in 2018 of a validation study of the Koukopou- lar patients led by our group [24], the three-factor solution of the los Mixed Depression Rating Scale, a new mixed mood rating scale RCTQ yielded the best fit indices when compared with a single [18]. “Racing and crowded thoughts” is one of the 14 items of the factor model proposed by our initial work [19] or an hypotheti- scale. The instructions for its rating are the following: “This symp- cal two-factor model based on the racing versus crowded thought tom is of cardinal importance. Note spontaneous reports before distinction. The short 13-item RCTQ, resulting from the removal of direct questioning. Rate on the basis of subjective experience that redundant and less discriminant items within the three factors, had thoughts/memories are more than usual, and/or thinking is accel- the strongest psychometric properties [24]. erated. Depressive ruminations are different: they are made up by The identification of racing and crowded thoughts in clinical few (often only one) depressive preoccupation.” practice is particularly difficult, hence highlighting the need of a During the last decade, few phenomenological studies have specific instrument targeting this symptom. In a study of patients focused on racing and crowded thoughts. In a qualitative analysis of seeking treatment for anxiety or mood symptoms and substance audiotaped interviews exploring subjective experience of thought use symptoms, comparison of racing thoughts as endorsed by overactivation in patients with mood disorders, our research group the patient when fulfilling the Mood Disorder Questionnaire [25] described five conceptual categories which characterized thought and racing thoughts as identified by the psychiatrists using the overactivation: sequential thought flow (i.e., one thought leading MDQ as a semi-structured interview, resulted in a low agreement to another), overstimulation, competition for resource allocation, score (kappa = 0.15). Similar results were found for irritability and unexpected/unexplained onset of thoughts, and association with distractibility symptoms, whereas excessive spending, increased mood and emotions [19]. In the same paper [19], a principal com- goal-directed activity and hypersexuality reached higher agree- ponent analysis of a newly developed 16-item auto-questionnaire ment scores [26]. to study thought overactivation indicated that a single component explained 55.9% of the variance with major and exclusive contribu- tions from 9 items. This single major component did not support a 3. Prevalence of racing/crowded thoughts in mood dualistic view of racing thought versus crowded thought and sug- disorders gested instead that subjective thought overactivation encompasses an overproduction of thoughts but also thoughts getting muddled, The aforementioned 2010 review [13] had put forward the syn- as well as the unrestrained/uncontrollable nature of thought flow. thesis published by Goodwin and Jamison in their 2007 book [1] These characteristics echo the ones revealed by the qualitative anal- and reported other original studies published afterwards whose ysis: thoughts are perceived as unexpected, too easily triggered, results were in agreement with Goodwin and Jamison’s results. difficult to inhibit and competing for resource allocation [19]. Thus, Based on 12 studies, Goodwin and Jamison [1] found that the mean consistent with phenomenological accounts of racing thoughts, prevalence of “flight of ideas/racing thoughts” in mania/hypomania

was 76%, with a 41 to 100% range. To our knowledge, there are no worst lifetime depressive episode was higher in men (19.5%) than recent studies with data about the prevalence of racing thoughts in in women (14.6%), and higher in atypical or agitated subtypes com- hypomania or mania. pared to melancholic subtypes. The link between racing thoughts The prevalence of racing thought/crowded thoughts in during depression and bipolar spectrum conditions was also sup- depressed patients was not addressed in Goodwin and Jamison’s ported by a study in depressed youth [38], showing an increased book [1]. The 2010 review [13] described data issued from original odds ratio for racing thoughts in depressed youth with high studies: the prevalence range was large in depressed patients; from familial risk for bipolar disorder compared to those with low famil- 5 to more than 50%. Such differences did not seem clearly related ial risk; subsyndromal hypomanic symptoms, particularly motor to the distinction bipolar versus unipolar depression and seemed hyperactivity, distractibility, and flight of ideas/racing thoughts, to be related to methodological differences that were also highly were higher in bipolar depressed youth, and discriminated bipo- correlated to authors’ specific interest. Benazzi’s huge personal con- lar depressed from unipolar depressed youth. Finally, one study tribution to the field of mixed depression and the unipolar/bipolar conducted during a pharmacological trial included patients (from depression distinction is a good illustration of this point [27]. The USA and Eastern Europe) with mixed depression as defined by a number of studies published during the last decade and provid- major depressive episode with two or three hypomanic symptoms ing data about the prevalence of racing/crowded thoughts during a (excluding distractibility, irritable mood and psychomotor agita- depressive episode is in sharp contrast with the lack of equivalent tion): the prevalence of the DSM-5 symptom of “flight of ideas studies in the field of mania: it reflects the growing research about or racing thoughts” was 66.8% [39]. It is noteworthy that in this mixed depression. We review below these recent studies about the study, “flight of ideas or racing thoughts” was the manic symptom prevalence of racing/crowded thoughts in depression. with the highest prevalence (preceding “more talkative or pressure In the NIMH Collaborative Depression Study, the prevalence to keep talking” and “distractibility” with respective prevalence at of racing thoughts/flight of ideas during bipolar major depressive 61.1 and 59.2%) [39], whereas in others studies with patients with episodes was 7.7% [28]. In the Systematic Treatment Enhance- major depression with and without mixed features it was not the ment Program for Bipolar Disorder, the prevalence of “racing case [28,30,32,36]. In conclusion, recent studies suggest a 30 to 70% thoughts/flight of ideas” in bipolar patients [29] was 17% in those prevalence of racing/crowded thoughts in mixed depression, much with a major depressive episode and 30% in those with a DSM-IV higher than a 4 to 12% prevalence in non-mixed depression. More- mixed episode (which required that both the criteria of a major over, the presence of racing/crowded thoughts is clearly associated depressive episode and of a manic episode were fulfilled) [7]. In a with the bipolar spectrum. study of the International Mood Network, in an international mixed It is also interesting to mention a study about the phenomenol- sample of bipolar and unipolar patients with a major depressive ogy of pre-(hypo)manic and pre-depressed prodromal symptoms episode, the global prevalence rate of racing or crowded thoughts [40]: “racing thoughts” is the second more frequent symptoms was 25% and when the sample was split between patient fulfilling occurring before the first (hypo)manic episode with a prevalence and not fulfilling the Koukopoulos criteria for mixed depression the of 78.6%, behind “feeling extremely energetic” (85.7%) and before” prevalence rates of racing and crowded thoughts was respectively physical agitation” (76.2%). In the same vein, the association of 46 and 4% in the two subsamples [30]. The 46% rate is close to the “racing thoughts” to “elation” or “irritability” in general population 48% rate of mixed depressive patients using the same Koukopou- probands who did not meet full criteria for hypomania or mania at los criteria found by the same author in a cohort of Italian patients study intake, was a significant predictor of a first episode of hypo- [31]. It is noteworthy that in this study racing and crowded thoughts mania or mania during the next three years [41]. These results were not related to nor triggered by ongoing antidepressant treat- echo those from a study of the treatment of bipolar depression ment [31]. In the BRIDGE study, based on a sample of depressed [42] whereby the relationship between manic items and treatment patients, the prevalence of racing thoughts was 11.8% whereas it emergent mania was explored using a factor analysis to identify was 59.9% in the subsample of patients fulfilling DSM-5 criteria for cluster of manic symptoms that covaried. Four factors were identi- depressive mixed states and 62.3% in the subsample of patients fied, but the motor/verbal activation factor, which included racing fulfilling the study specific Research-Based-Diagnostic-Criteria for thoughts, was the only one significantly related to treatment emer- depressive mixed states [32]. When a cluster approach was used gent mania. with the BRIDGE study data, it distinguished a first cluster of non- mixed depression and a second cluster of mixed depression: the prevalence of racing thoughts was respectively 3.9 and 34.4% in the 4. Association of racing/crowded thoughts with other two clusters [33]. Yet, when clinical features predicting cluster label affective symptoms were identified using a stepwise logistic regression model, racing thoughts was not one of the seven symptoms that best predicted In the 2010 review [13], studies using principal component cluster membership [33]. In the BRIDGE study, the prevalence of analysis, in manic patients showed convergent results: racing racing thoughts, as for most hypomanic symptoms, was higher in thoughts was usually found in a factor including other classical patients with a more recurrent depressive disorder: 12.1% in sub- manic symptoms such as elated mood, increased energy, activ- jects with more than 3 lifetime episodes versus 7.4% with patients ity, self-esteem and social contact as well as flight of ideas and with 3 or less episodes [34], a difference that is mainly linked to the acceleration of speech. However, one study by Benazzi using the positive association between recurrence and markers of bipolar dis- Mood Diagnostic Questionnaire (MDQ), a self-report questionnaire order. In the same BRIDGE study, what has been found for recurrent screening past hypomanic or manic episode [25], suggested that depression was also observed for borderline personality disorder: racing thoughts was associated with irritability and it was not a positive association with markers of bipolar disorder and a higher related to increased energy and activity [43]. In a study of the prevalence of racing thoughts when a borderline personality dis- Brazilian version of the MDQ [44], racing thoughts was the second order is present (30.5 versus 10.5%) [35]. In a Japanese sample higher loaded item after irritability on the first factor revealed by of major depressive episode patients, the prevalence of flight of principal component analysis, a second factor being loaded mainly ideas/racing thoughts was 36.4%, and it was lower in the subgroup by “more energy” and “more active”. Such results echo other results of major depressive disorder patients (20.0%) than in the subgroup which were not included in the 2010 review [13]. In an extended of bipolar II/bipolar not otherwise specified patients (58.7%) [36]. In sample, Benazzi [45] found similar results to his aforementioned a Brazilian study [37], the prevalence of racing thoughts during the initial study [43]: factor analysis of hypomanic symptoms during

hypomanic episodes showed that the “racing/crowded thoughts” in schizophrenia is a “slow, steady slippage”, whereas in mania item was part of a second factor associated to “irritable mood” “flight of ideas is a derailment that occurs rapidly in the context and “distractibility” distinct from a more classic first factor which of pressured speech” [52]. included “elevated mood”, “inflated self-esteem”, “decreased However in her clinical work, Andreasen [53] showed that need to sleep”, “talkativeness” and “overactivity”. In a Honk-Kong thought disorders in schizophrenia and mania were qualitatively validation study of the Mood Diagnostic Questionnaire (MDQ), similar; their severity only varied along a spectrum: schizophrenic principal component analysis indicated that “racing thoughts” was and manic thought disorders being respectively the most severe included in a “euphoria-irritability-racing thoughts” factor distinct and less severe forms. Consistently, a recent systematic review from an “energized-activity” factor, and a “risky behavior” factor and meta-analysis of formal thought disorder in schizophrenia and [46]. To summarize, recent studies suggest that racing thoughts bipolar disorder [54] supported the view that, in the acute inpatient are more associated with irritability than energy and activity samples, there was no significant difference in the severity of pos- increase. Thus, racing thoughts are related to the “dark” side and itive formal thought disorders between schizophrenia and bipolar not only the “sunny” side of hypomania. This lends some indirect disorder patients. support to Kraepelin and Weygandt’s proposal [4] that mood dis- Concerning the question of anxiety, our own studies have con- orders include three distinct areas of psychic functioning (affect, firmed the view developed in the 2010 review [13] that there was a psychomotor activity and associative thinking) and psychomotor link between racing thoughts and anxiety both in the general pop- activity and associative thinking may be dissociated in hypomania. ulation [20] and in mood disorders patients [19,24]. This link could The 2010 review [13] mentioned only one study of hypomanic rely on a common dimension of hyperarousal in anxiety states and symptoms in depressed patients using principal component anal- in hypomanic or mixed bipolar states. Concerning ADHD, prelim- ysis [47]: racing thought appeared in the only hypomanic factor inary results from our group [55] have shown that RCTQ score alongside other behavioral hypomanic symptoms such as logor- was significantly higher in ADHD patients compared to controls rhea, increased activity and social contact. We have found several and even compared to manic patients. Racing thoughts in ADHD recent studies concerning the association of racing thoughts with patients were more severe at bedtime and correlated positively other symptoms during manic/hypomanic states. For instance, one with insomnia, and with mood instability, two clinical symptoms study reported the association of racing thoughts with other hypo- highly prevalent in ADHD. Moreover, there is a high rate of associ- manic symptoms during a depressive episode [48]; an exploratory ation between ADHD and bipolar disorder [56]. Last but not least, factor analysis of hypomanic symptoms identified three factors: we also found that patients with primary insomnia have high RCTQ factor 1 (“elation-disinhibition-increased goal directed activity”), score, with a predominance of racing thought at bedtime [57]. Thus, factor 2 (“risk-taking-impulsivity-substance use”) and factor 3 racing and crowded thoughts are a phenomenological dimension at (distractibility–irritability), racing thoughts was included in this the heart of mood disorders but also seem to be at the intersection last factor. Of note, in a study of former inpatients who commit- of other related psychopathological dimensions such as anxiety, ted suicide [49] – (60% with bipolar disorder, 22% with a major arousal, attention and sleep disorders. Finally, in this section, we depressive disorder or episode, 7% with a schizoaffective disorders must include the perspective of comorbidities in bipolar disorder, and more than 80% with depression –, at the time of their suicide), even if the data are limited. We found a study comparing bipolar racing thoughts were identified in 53.1% of the patients; such preva- disorder in youth with and without high-functioning autism spec- lence was lower than the prevalence of suicidal thinking (74.0%) trum disorder (HF-ASD): racing thoughts and distractibility were or inner tension (54.2%) but higher than the prevalence of delu- the only two manic symptoms significantly more prevalent at study sions (38.5%), aggressive behavior (31.2%) or psychomotor agitation intake in patients with HF-ASD as compared with patients without (30.2%). This suggests that racing thoughts could be a mixed-related HF-ASD [58]. Maybe ADHD which is highly associated with HF-ASD feature that links depression and risk of suicide [50]. [59] could contribute to this difference.

5. Racing/crowded thoughts and other illnesses

The 2010 review [13] stressed that neither the DSM-IV, nor the ICD-10, mentioned the concept of racing thoughts in any other 6. Racing/crowded thoughts and depressive rumination categories of mental disorders. This is not any different from the newly-defined DSM-5 categories [14]. Yet, as mentioned in the The 2010 review [13] proposed, yet without empirical data to 2010 review [13], racing/crowed thoughts are frequently reported support this hypothesis, that in mixed depressive states crowded by patients presenting with other mental disorders. In anxiety and thoughts should be clearly distinguished from rumination. The particularly in panic attacks, racing thoughts are a frequent symp- authors claimed that patients with rumination seemed able to tom related to hyperarousal. The 2010 review [13] also reported report the contents of their rumination, contrary to patients with one study of racing thoughts in borderline incarcerated women crowded thoughts who were overwhelmed by many ideas with [51] and highlighted the importance of this finding, given the high many themes and felt unable to “catch their thoughts” [13]. rates of comorbid borderline personality disorders in bipolar dis- Our recent studies confirmed the independence of the concept order. The same applies to attention deficit/hyperactivity disorder of racing/crowded thought and the concept of rumination by show- (ADHD) [13], although the 2010 review points to the fact that ing no relationship between the RCTQ score and the two subscales racing thoughts have been predominantly associated with bipo- scores of the Ruminative Response Scale State version [60] nei- lar disorder rather than ADHD. Finally, concerning schizophrenia, ther in a general population sample [20] nor in a clinical sample the review pointed to the ambiguity linked to the use of the term [24]. Besides, a French study [61] showed that the level of depres- flight of ideas [13]. Whereas racing thoughts could be considered sion in subjects initially admitted as emergencies for acute anxiety as the subjective equivalent of the flight of ideas in the field of depressive disorders and/or suicide attempts was correlated with mood disorders, this is different in schizophrenia. Andreasen [52] increased ‘flow of thoughts’, but not number of thoughts; these used the concept of “derailment” suggesting that it is the loosening two dimensions were elegantly assessed by filling a drawing of an of the degree of association between thoughts, not their accelera- aquarium to reflect the number of thoughts (by drawing fish) and tion that is crucial to flight of ideas in schizophrenia. Derailment cognitive turmoil (by drawing wavy lines).

7. Synthesis and perspective for future research hence suggesting that it is possible to experimentally induce the phenomenon of linear racing thoughts [67]. The 2010 review [13] proposed a theoretical model distinguish- ing racing and crowded thoughts. Racing thoughts in hypomania 8. Conclusion and mania were conceptualized as linear racing thoughts and the result of an increased production of new thoughts with a normal There has been ten years since the publication of our initial the- ability to inhibit previous thoughts. Crowded thoughts in mixed oretical reappraisal focusing on the phenomenology of racing and depression were conceptualized as resulting from an increased pro- crowded thoughts [13]. During this decade, mixed depression has duction of new thoughts, a common process with linear racing become a major research interest in the field of mood disorders, thought, associated to a decreased inhibition of previous thoughts, and so has the focus on racing thoughts as a possible distinguish- a process that would be common to the ruminations [13]. In other ing symptom between mixed and non-mixed types of depression. words, crowded thoughts could be a hybrid of racing thoughts and This makes this update on this key symptom all the more needed. ruminations. In 2012, Desseilles et al. [62] proposed a slightly more The present paper confirms and extends the understanding complex perspective based on a three, rather than two, dimen- of racing and crowded thoughts. The dichotomist view of rac- sional model of thoughts in mood disorders: to the dimension of ing versus crowded thoughts, although not refuted, seems to be thought quantity and emotional valence of thought, they added the more complex than initially conceptualized, as it does not fully dimension of thought associative pattern which could be charac- reflect the distinction between hypomania and mixed depres- terized as narrow or broad. In the current review, we propose an sion. Studies published during the last decade have also shown approach slightly different from the 2010. Linear racing thoughts that racing/crowded thoughts are strongly associated with mixed could be limited to hypomanic states whereas, as already described depression as compared with non-mixed depression, and that, in by Goodwin and Jamison [1], in severe manic and in mixed manic hypomania, they are more associated with irritability than with states, rapid thinking proceeds to fragmented and disjointed think- the typical symptoms of energy and activity increase, on the one ing phenomenologically closer to crowded thoughts as reported hand, and that they are distinct from rumination, on the other hand. in mixed depression. This perspective does not abandon one of Yet, although central to mood disorders, racing/crowded thoughts the key proposals of the previous model whereby racing thoughts appear to be associated with anxiety as well as ADHD and insomnia. become crowded thoughts due to an imbalance between the emer- Racing and crowded thoughts should thus be viewed in a dimen- gence of new thoughts in consciousness and the cognitive ability sional perspective, as an important facet of mind activity within to grasp them, acknowledge them and put them aside to pass to and beyond mood disorders. Given its good psychometric proper- the next. In mixed depression, this disequilibrium arises from the ties, our newly developed self-report questionnaire, the Racing and increase of new thoughts linked to the hypomanic psychic exci- Crowded Thoughts Questionnaire [20], may be a reliable means of tation and the difficulty to discard negative thought linked to the clinically assessing this important and frequent symptom. depressive ruminative process. In hypomania or moderate mania, the cognitive ability to treat new thought parallels the acceler- Disclosure of interest ation of thoughts production. By contrast, in more severe manic states, the cognitive ability to treat new thoughts is overwhelmed The authors declare that they have no competing interest. by an excessive acceleration of thought production. This mirrors another well-known clinical aspect [1,3]: the inverse U-shaped References relationship of the level of productivity/creativity and the severity of hypomania/mania. 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