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Electric Stimulation of the Medial Forebrain Bundle Influences Panther et al. BMC Neurosci (2019) 20:20 https://doi.org/10.1186/s12868-019-0503-y BMC Neuroscience RESEARCH ARTICLE Open Access Electric stimulation of the medial forebrain bundle infuences sensorimotor gaiting in humans Patricia Panther1,2, Maria Kuehne3, Jürgen Voges1, Sven Nullmeier4, Jörn Kaufmann3, Janet Hausmann3, Daniel Bittner3, Imke Galazky3, Hans‑Jochen Heinze3,6, Andreas Kupsch1,3,5† and Tino Zaehle3*† Abstract Background: Prepulse inhibition (PPI) of the acoustic startle response, a measurement of sensorimotor gaiting, is modulated by monoaminergic, presumably dopaminergic neurotransmission. Disturbances of the dopaminergic system can cause defcient PPI as found in neuropsychiatric diseases. A target specifc infuence of deep brain stimula‑ tion (DBS) on PPI has been shown in animal models of neuropsychiatric disorders. In the present study, three patients with early dementia of Alzheimer type underwent DBS of the median forebrain bundle (MFB) in a compassionate use program to maintain cognitive abilities. This provided us the unique possibility to investigate the efects of diferent stimulation conditions of DBS of the MFB on PPI in humans. Results: Separate analysis of each patient consistently showed a frequency dependent pattern with a DBS‑induced increase of PPI at 60 Hz and unchanged PPI at 20 or 130 Hz, as compared to sham stimulation. Conclusions: Our data demonstrate that electrical stimulation of the MFB modulates PPI in a frequency‑dependent manner. PPI measurement could serve as a potential marker for optimization of DBS settings independent of the patient or the examiner. Keywords: Prepulse inhibition, PPI, Medial forebrain bundle, Deep brain stimulation, DBS, Reward system, Neuromodulation, Alzheimer’s disease Background like schizophrenia, obsessive compulsive disorders, Hun- Prepulse inhibition (PPI) of the acoustic startle response tington’s and Parkinson’s disease (PD) [4, 5, 31, 36, 44]. (ASR) is a physiological and operational measure of the Also dementia of Alzheimer type (AD) is discussed to pre-attentive fltering process known as sensorimo- diminish PPI [14, 27, 38]. Measurement of PPI is charac- tor gating [20]. PPI describes a reduction in the star- terized by adequate face, predictive, and construct valid- tle response amplitude, if an acoustic startling pulse ity [35], but can be also modulated by attention and drugs is preceded by a non-startling stimulus (prepulse) at [9, 17]. Additionally, PPI has been shown to be directly approximately 30 – 500 ms [12, 32]. Te weak prepulse infuenced by monoaminergic agents and is altered in stimulus is thought to activate a pre-attentional gating diseases associated with dopaminergic dysfunction [5, mechanism that inhibits the startle response. Defcits in 11]. Further, baseline PPI is suggested as an important PPI can be found in several neuropsychiatric disorders determinant of the efect of dopamine agonists on PPI [1]. Although it does not require learning, the expression *Correspondence: [email protected]; [email protected] of PPI is regulated by higher cognitive processes [20]. A †Andreas Kupsch and Tino Zaehle have equal contribution as senior potential link between PPI expression and cognitive per- authors 3 Department of Neurology, University Hospital of Magdeburg, Leipziger formance has been suggested, such that poor PPI may Str. 44, 39120 Magdeburg, Germany predict cognitive impairments [2]. With regard to the lat- Full list of author information is available at the end of the article ter, patients with PD, which show higher levels of PPI, are © The Author(s) 2019. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creat iveco mmons .org/licen ses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creat iveco mmons .org/ publi cdoma in/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Panther et al. BMC Neurosci (2019) 20:20 Page 2 of 9 reported to perform better on cognitive measures, atten- consent for investigations addressing the infuence of tion and processing speed than patients with lower levels deep brain stimulation (DBS) of the MFB on PPI. of PPI [44]. Te median forebrain bundle (MFB) is a complex com- Participants position of monoaminergic fbre systems connecting Tree patients sufering from mild Alzheimer’s disease midbrain and forebrain areas (Fig. 1a, b). It is involved (patient #1, female, age 79, Mini-Mental State Examina- in processing the dopamine dependent reward efect of tion (MMSE): 27; patient #2, female, age 70, MMSE: 22; electrical self-stimulation [42]. Dopaminergic modula- patient #3, male, age 70, MMSE: 17; all three patients tion has been discussed as a therapeutic option to restore were right handed) were ofered bilateral DBS of the altered cortical plasticity in AD [19]. Conceivably, elec- MFB (Fig. 1). Tis treatment option is not a standard, trical stimulation of the MFB modulates dopaminergic but a novel experimental approach in Alzheimer’s dis- pathways and could represent a potential therapeutic ease. Terefore DBS of the MFB was ofered to these approach in AD, which we ofered to three AD patients three patients as an individual treatment as compassion- as compassionate use. ate use to improve cognition in AD. Te patients were DBS allows focal and reversible neuromodulation. Data able to understand the experimental and pilot character supports its efcacy in movement disorders, but also psy- of the method and the risk of the medical intervention chiatric diseases [15]. Finding the best stimulation setting and gave their written consent to participate in the study; in patients with a DBS-System can be challenging, espe- continued ability to participate in the present study has cially if DBS does not exert rapid therapeutic response on been clinically verifed by continued scientifc compli- the symptoms of the disease. Terefore, it is necessary ance of the included patients. Furthermore, stimula- to fnd tools indicating a change in the cerebral network tion of MFB additionally ofered the unique opportunity activity which are easily and fast performed and react to scientifcally explore the modulation of PPI by DBS, quickly on changes of the programming. which was included in the written informed consent. Since it was shown that pharmacologic manipulations Patients were tested in MMST to evaluate the sever- of the dopaminergic systems alter sensorimotor gating ity of dementia. Additionally, to exclude unsystematic [5, 11, 24, 33], we investigated if PPI can be infuenced side efects during the postoperative stimulation period by DBS of the MFB in a stimulation frequency dependent of 3–6 days, we assessed an extensive cognitive testing manner, to elucidate its potential for optimisation of DBS battery to ensure that our experimental manipulation setting. did not harm the patients. Te cognitive tests compris- ing visual learning, short delayed match to sample task, reward paradigms, Mini-Mental State Examination, Alz- Methods heimer’s Disease Assessment Scale Cognition, geriatric Ethical standards of Human and Animal Rights were depression scale, tests for attentional performance, and adhered (including the Helsinki Declaration of 1975, as spatial memory tests, all of them did not change signif- revised in 2000 and 2008) and the experimental design cantly during the short postoperative stimulation period was approved by the local ethical committee (University of 3–6 days. Finally, to exclude the possibility of a hearing of Magdeburg, Germany; reference numbers 07/12 and loss all patients were neurologically examined. Patients 131/13). In addition, the patients gave their informed were recruited from the Departments of Neurology and (See fgure on next page.) Fig. 1 Schematical drawing and fber reconstructions of the medial forebrain bundle. Schematical drawing (a) and fber reconstruction based on difusion imaging of a healthy control (b) illustrating the main projections of the fasciculus telencephali (medial forebrain bundle, MFB) are shown. Further, individual MFB reconstructions, with the corresponding electrode position for only the left side are shown for patient 1 (c sagittal‑, d axial‑, e coronal sections), patient 2 (f, g, h) and patient 3 (i, j, k). The activated contact is marked in red. The MFB consists of thin, loosely arranged ascending and descending fbers extending from septal area (SP) to the mesencephalic tegmentum. Along this route it traverses the lateral hypothalamic area (ALH) and splits into a smaller medial and larger lateral stream at transitional zone of diencephalon and midbrain. The medial stream (mSTR) passes through the parts of the mesencephalic and rhombencephalic tegmentum, connecting the hypothalamic centers with raphe nuclei and medial reticular formation. On the other hand, ascending serotonergic fbers from the dorsal (DR) and medial raphe (MnR) nuclei reach the ALH and a variety of diencephalic and telencephalic centers. The lateral stream (lSTR) connects the central nucleus of the amygdala (CeA) and hypothalamic areas with diferent brain stem areas in pons and medulla oblongata. It further comprises fbers ascending from dopaminergic ventral tegmental area (VTA) and substantia nigra pars compacta (SNc), but also fbers
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