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Temporal Lobe Syndromes: Disturbances of Hearing and Vestibular Functions

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Temporal Lobe Syndromes: Disturbances of Hearing and Vestibular Functions TEMPORAL LOBE SYNDROMES: DISTURBANCES OF HEARING AND VESTIBULAR FUNCTIONS CLASS : M.A SEMESTER-II PAPER : CC-6 (NEUROPSYCHOLOGY) UNIT-4 RAJNISH KUMAR ASSISTANT PROFESSOR DEPT. OF PSYCHOLOGY G.D.COLLEGE • The temporal lobes sit behind the ears and are the second largest lobe. • The temporal lobe is the region where sound is processed and, not surprisingly, it is also a region where auditory language and speech comprehension systems are located. • The auditory cortex is located on the upper banks of the temporal lobe and within the sylvian fissure. Just posterior to the auditory cortex is Wernicke's area for speech comprehension. Damage to the temporal lobes can result in: • Difficulty in understanding spoken words (receptive aphasia) • Disturbance with selective attention to what we see and hear • Difficulty with identification and categorization of objects • Difficulty learning and retaining new information • Impaired factual and long-term memory • Persistent talking • Difficulty in recognizing faces (prosopagnosia) • Increased or decreased interest in sexual behaviour • Emotional disturbance (e.g. Aggressive behaviour) • Auditory radiations run from the medial geniculate body to the auditory cortex ( areas 41 and 42) in the superior temporal gyrus. • Hearing is represented bilaterally in the temporal lobes (contralateral predominance). • Electrical stimulation of auditory area leads to vague auditory hallucination (tinnitus, sensation of roaring and buzzing ), and adjacent areas causes vertigo and a sensation of unsteadiness. • Unilateral destruction of the auditory cortex lead to difficulty in sound localization and a bilateral decrease of auditory acuity. • Bilateral disease lead to cortical deafness (may be unaware of their deficits). • Involvement of vestibular areas may cause difficulty in equilibrium and imbalance. CENTRAL OR CORTICAL DEAFNESS • The first description of this disorder is attributed to Wernicke and Friedlander (1883). • They reported a patient with bilateral temporal-lobe lesions but with no apparent damage to the hearing organ, who showed no awareness of sounds. • Patients appear deaf, although some reflex responses such as turning toward a sudden loud sound may be preserved. • Cortical deafness is essentially the combination of word deafness and auditory agnosia. • It is characterized by an inability to interpret either verbal or nonverbal sounds with preserved awareness of the occurrence of sound (e.g., by a startle reaction to a clap). • The term “deaf-hearing” has also been used for cases who show some response to sound, postulated to be reflexive, but with no sound awareness. PURE WORD DEAFNESS • Pure word deafness is a rare subtype of central deafness. • This disorder is defined as disturbed auditory comprehension without difficulties with visual comprehension. • Patients characteristically have fluent verbal output, severe disturbance of spoken language comprehension and repetition, and no problems with reading or writing. • Nonverbal sounds are correctly identified. • Patients can communicate by reading, writing, and lip-reading. • Word deafness results mostly from bilateral temporal lesions interrupting the connections between the two primary auditory cortices to Wernicke's area. AUDITORY AGNOSIA • Auditory agnosia, another rare subset of central deafness, is typified by relatively normal pure‐tone hearing on audiometry but inability to interpret (recognize) nonverbal sounds such as the ringing of a telephone. • Inability to interpret nonverbal sounds but preserved ability to interpret speech may be a result of a right hemisphere lesion alone. • Amusia is a particular type of auditory agnosia in which only the perception of music is impaired. • PHONAGNOSIA is the inability to identify a speaker by his or her voice. • AMUSIA is a disorder of music perception such as impaired ability to recognize melodies. • It is commonly associated with right temporal lesions, but left-sided lesions also may produce musical perception disorders, especially melody and written music identification. • Sometimes nondominant or bilateral temporal lobe damage can cause an agnosia for environmental sounds. • TINNITUS is the false perception of a sound, or the perception of a sound that is not normally perceived, such as the pulse. AUDITORY HALLUCINATIONS • Auditory hallucinations consist of an illusion of a complex sound such as music or speech. • These hallucinations most commonly occur as a result of an injury to the superior temporal auditory association areas. • Penfield discovered that stimulating this area induced an auditory sensation that seemed real to patients. • Auditory hallucinations can also occur as a result of temporal lobe seizure. Vestibular System • The two major cortical functions of the vestibular system are spatial orientation and self-motion perception. • These functions, however, are not exclusively vestibular; they also rely on visual and somatosensory input. • All three systems (vestibular, visual and somatosensory) provide us with redundant information about the position and motion of our body relative to the external space. • Although the vestibular cortex function is distributed among several multisensory areas in the parietal and temporal cortices, it is also integrated in a larger network for spatial attention and sensorimotor control of eye and body motion in space. • The vestibular system contributes to optimize visual acuity during head motion, enhances balance control, and allows detection of self-motion and orientation relative to gravity. • Vertigo is a false sensation of movement that is usually caused by disorders of the vestibular system, including the inner ear and/or parts of the central nervous system involved in processing of vestibular signals. • Vertigo is often accompanied by imbalance as well as secondary symptoms such as nausea and fatigue. • The temporal lobe contains the vestibular cortex in the posterior part of the superior temporal sulcus, and lesions in this region lead to contralateral tilts of the subjective visual vertical (Brandt and Dietrich, 1994) and fixation suppression of caloric-induced nystagmus (carmichael et al., 1954). • Patients with lesions of this area may also have a defect in memory-guided saccades after a vestibular (rotational) stimulus (Israel et al., 1995). • Lesions in the parahippocampal region of the medial temporal lobe have been found to impair spatial working memory in the memory-guided saccadic paradigm (muri et al., 1994). .
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