Speech rate as a sticky switch: a multiple lesion case analysis of mutism and hyperlalia

Though it has long been known on the basis of clinical associations and serendipitous observation that speech rate is related to mood and psychomotor baseline, it is less known that speech rate is also related to libido and to immune function. We make the case for a bipolar phenomenon of "psychic tonus," encompassing all these dimensions. The elated, agitated, libidinal, immunofacilitated, and talkative pole is an "approach" disposition primarily activated by the normal left hemisphere-especially, though not exclusively, its frontal lobe. The dejected, lethargic, delibidinized, immunosuppressed, and mute pole is an "avoidance" disposition primarily activated by the normal right hemisphere-especially, though not exclusively, its frontal lobe. In support of this proposed model, we present new evidence, via meta-analysis of previously published single lesion case reports, of a highly significant association between right hemisphere lesions and non-aphasic hyperlalia, and between left hemisphere lesions and non-aphasic mutism.     

卒中部位及局部脑血流量对智力的影响

用长谷川智力测定量表法测定了１８９例卒中患者的智力,分析了病变部位、脑萎缩及局部脑血流量（ｒＣＢＦ）对智力的影响．其中６９例患者长谷川分数低于２１．５分．当病变位于左半球时,属痴呆或可疑痴呆者达４２．９％;而病变位于右半球时,仅２３．１％属痴呆及可疑痴呆．ｒＣＢＦ与长谷川分数之间的相关分析显示：左额、右颞及左顶叶的ｒＣＢＦ与长谷川分数呈极显著正相关．提示左半球在智力活动中起主导作用．脑萎缩亦是影响智力的因素．     

Spatial neglect, Balint-Homes' and Gerstmann's syndrome, and other spatial disorders

Brain-damaged patients with lesion or dysfunction involving the parietal cortex may show a variety of neuropsychological impairments involving spatial cognition. The more frequent and disabling deficit is the syndrome of unilateral spatial neglect that, in a nutshell, consists in a bias of spatial representation and attention ipsilateral to of extrapersonal, personal (ie, the body) space, or both, toward the side of the hemispheric lesion. The deficit is more frequent and severe after damage to the right hemisphere, involving particularly the posterior-inferior parietal cortex at the temporo-parietal junction. Damage to these posterior parietal regions may also impair visuospatial short-term memory, which may be associated with and worsen spatial neglect. The neural network supporting spatial representation, attention and short-term memory is, however, more extensive, including the right premotor cortex. Also disorders of drawing and building objects (traditionally termed constructional apraxia) are a frequent indicator of posterior parietal damage in the left and in the right hemispheres. Other less frequent deficits, which, however, have a relevant localizing value, include optic ataxia (namely, the defective reaching of visual objects, in the absence of elementary visuo-motor impairments), which is typically brought about by damage to the superior parietal lobule. Optic ataxia, together with deficits of visual attention, of estimating distances and depth, and with apraxia of gaze, constitutes the severely disabling Balint-Holmes' syndrome, which is typically associated with bilateral posterior parietal and occipital damage. Finally, lesions of the posterior parietal lobule (angular gyrus) in the left hemisphere may bring about a tetrad of symptoms (left-right disorientation, acalculia, finger agnosia, and agraphia) termed Gerstmann's syndrome, that also exists in a developmental form.     

Parietal versus temporal lobe components in spatial cognition: Setting the mid‐point of a horizontal line

Recent anatomo‐clinical correlation studies have extended to the superior temporal gyrus, the right hemisphere lesion sites associated with the left unilateral spatial neglect, in addition to the traditional posterior‐inferior‐parietal localization of the responsible lesion (supramarginal gyrus, at the temporo‐parietal junction). The study aimed at teasing apart, by means of repetitive transcranial magnetic stimulation (rTMS), the contribution of the inferior parietal lobule (angular gyrus versus supramarginal gyrus) and of the superior temporal gyrus of the right hemisphere, in making judgments about the mid‐point of a horizontal line, a widely used task for detecting and investigating spatial neglect. rTMS trains at 25 Hz frequency were delivered over the inferior parietal lobule (angular gyrus and supramarginal gyrus), the superior temporal gyrus and the anterior parietal lobe of the right hemisphere, in 10 neurologically unimpaired participants, performing a line bisection judgment task. rTMS of the inferior parietal lobule at the level of the supramarginal gyrus brought about a rightward error in the bisection judgment, ipsilateral to the side of the rTMS, with stimulation over the other sites being ineffective. The neural correlates of computing the mid‐point of a horizontal segment include the right supramarginal gyrus in the inferior parietal lobule and do not extend to the angular gyrus and the superior temporal gyrus. These rTMS data in unimpaired subjects constrain the evidence from lesion studies in brain‐damaged patients, emphasizing the major role of a subset of relevant regions.     

Opposed left and right brain hemisphere contributions to sexual drive: a multiple lesion case analysis

Brain topographical studies of normal men have have shown that sexual excitation is asymmetric in the brain hemispheres. Group studies of patients with unilateral epileptic foci and other studies of patients with unilateral brain lesions have come to the same conclusion. The present study reviewed previously published single case reports of patients with frank hypo or hypersexuality subsequent to a unilateral brain lesion. Hyposexual patients tended to have left hemisphere lesions (primarily of the temporal lobe), and hypersexual patients tended to have right hemisphere lesions (primarily of the temporal lobe) (p < 0.05). We interpret this double dissociation as part of a more general phenomenon of psychic tone similarly dissociated with regard to hemispheric control, including mood, psychomotor baseline, speech rate, and even immunity. The behavioral significance of this psychic tone is to modulate approach versus avoidance behavior.     

Gerstmann syndrome without aphasia: a longitudinal study

A case of "pure" and complete Gerstmann syndrome resulting from a focal vascular lesion in the posterior parietal area of the left hemisphere and not associated with aphasic disorder or general mental impairment is described. The initial symptom presentation of this patient supported the concept of the autonomous nature of the Gerstmann aggregate but longitudinal findings suggested that these symptoms did not in fact represent a coherent syndrome.     

Evidence for a Disturbance of the Body Schema in Neglect

Subjects with left neglect often fail to use and, in some instances, recognize the left side of the body. We performed a series of investigations to determine if this deficit is, at least in part, attributable to an impairment in the “body schema,” an internal three-dimensional, dynamic representation of the spatial and biomechanical properties of one's body. First, subjects were shown a series of pictures of a single hand and asked to determine if the stimulus was a right or left hand. Subjects with neglect but not other subjects with brain lesions identified pictures of left (contralesional) hands significantly less reliably than pictures of right hands. On the basis of evidence demonstrating that the identification of pictured hands involves the matching of the stimuli to an on-line mental representation of one's body, these data suggest that neglect may be associated with a disruption of, or failure to attend to, the body schema. Data from subsequent investigations contrasting patients with left neglect and Gerstmann's syndrome argue for a distinction between a body schema and a “body image,” or conceptual representation of the body which articulates with language.     

An investigation of immune system disorder as a "marker" for anomalous dominance

Geschwind and Galaburda (1987) proposed that immune disorder (ID) susceptibility, along with left handedness and familial sinistrality (FS), is a "marker" for anomalous dominance. The theory predicts lesser left lateralization for language processes, lessened left hemisphere abilities, and enhanced right hemisphere abilities. We assessed language laterality (dichotic consonant vowel task) and performances on spatial and verbal tasks. Subjects were 128 college students. The factors of handedness, sex, FS, and immune disorder history (negative or positive) were perfectly counterbalanced. Left-handers were significantly less lateralized for language and scored lower than right-handers on the spatial tasks. Females scored lower on mental rotation than males, but performed comparably to males on the spatial relations task. The only effect of ID was by way of interaction with FS on both spatial tasks--subjects who were either negative or positive on both FS and ID status factors scored significantly higher than subjects negative for one but positive for the other factor. A speculative explanatory model for this interaction was proposed. The model incorporates the notion that FS and ID factors are comparably correlated, but in opposite directions, with hormonal factors implicated by other research as relevant for spatial ability differences. Finally, no support for the "anomalous dominance" hypothesis predictions was found.     

Apparent shift in visual field preference after unilateral stroke

Patients with either a left- or a right-hemisphere stroke lesion scored higher in tasks of word-picture matching and of nonverbal shape matching when information was presented tachistoscopically (120 msec) to the visual field (VF) projecting to their undamaged hemisphere. Left-hemisphere stroke patients (n = 13) were dissociated from right-hemisphere stroke patients (n = 15) by low word recognition from memory and by low right VF but nearly normal left VF accuracy in word-picture matching or shape matching; the former appeared to rely upon processing of word meaning by the right hemisphere. In contrast, right-stroke patients had higher right than left VF scores in both tasks, and their discrimination of nonverbal shapes via the right VF was not different from that of controls (n = 15). Preferred processing by the VF projecting to the undamaged hemisphere appeared as a shift in perceptual asymmetry but may indicate, in support of a "direct access" model, that each hemisphere responds more or less efficiently to word and to nonverbal shape discriminations.     

Affective Priming Effects in the Left and Right Cerebral Hemispheres in Patients With Alzheimer's Disease

Alzheimer’s disease (AD) patients and control subjects were tested in an affective priming paradigm associated with an affective discrimination task. Two pictures, one affectively positive or affectively negative and the other neutral, were presented simultaneously in the right and in the left visual fields; the participants had to decide which of the two pictures was the most affectively positive or negative. The target pictures were preceded by a prime picture that was either affectively positive, affectively negative, or neutral. The principal result was the observation, in AD patients as well as in control subjects, of negative affective priming effects for targets presented in the right hemisphere, and of positive affective priming effects for targets presented in the left hemisphere. The presence of affective priming effects suggests that AD patients have no particular deficit in the automatic activation of emotional information; the fact that priming effects were also observed for targets presented in the left hemisphere showed that AD patients probably have no left hemisphere deficit in the automatic activation of emotional information. However, in AD patients, affective priming effects were significant with negative targets but not with positive targets, which could suggest that AD patients processed positive targets in a more semantic way than negative targets.     

Impairments of nonverbal oral movements after left hemisphere damage: A followup analysis of errors

Acquisition of a task requiring the imitation of a series of nonverbal oral movements is most severely impaired in patients with aphasic disturbance. However, nonaphasic patients with left hemisphere damage also perform more poorly than patients with right hemisphere damage or normal control subjects. Analysis of the errors made on the multiple oral movements task reveals that left, but not right, hemisphere damage is highly associated with perseverative responses. Patients with right hemisphere damage do not differ significantly from normal control subjects in the acquisition of or in the type of errors made on the task. It is suggested that the left hemisphere plays an important role in the control of nonverbal oral movement production.     

Lesion localization in acquired deficits of emotional expression and comprehension

This study investigated the relationship between intrahemispheric location of lesion and disturbances of emotional expression and comprehension. Twenty-eight right hemisphere strokes, 18 left hemisphere strokes, and 20 controls were examined on a standardized test of the expression, repetition, and comprehension of emotional prosody as well as the visual recognition of emotional situations and faces. The patients were classified into aprosodic syndromes according to the test scores. The lesions were independently traced, and overlapped for each aprosodic syndrome. The results, for lesions in either hemisphere, indicated involvement of the basal ganglia most frequently in aprosodic syndromes followed by anterior temporal lobe and insula lesions. Basal ganglia damage was also seen most frequently in patients with impaired comprehension of emotional facial expressions and situations. The anterior temporal lobe was also frequently involved in patients with such deficits. The basal ganglia emerged as a structure of particular importance in the mediation of emotional expression and comprehension.     

Hemisphere Inactivation and Mood-State Changes

Mood-state changes were studied during a sodium Amytal testing procedure in epilepsy patients with unilateral temporal lobe foci. The results showed that inactivation of the left hemisphere, but not the right hemisphere, produced a negative mood state. This decline in mood was not specifically related to side of focus or sex. As expected, the inactivation of either hemisphere also lead to an impairment in memory performance. This impairment was somewhat worse during a left than a right hemisphere inactivation. Furthermore, patients with left hemisphere foci showed a lower memory performance than patients with a right-hemisphere lesion. These results suggest (a) a hemispheric specialization for emotion that underlie changes in mood and (b) a discrepancy between mood states at encoding (during inactivation) and retrieval (after inactivation).     

A Voxel-based lesion study on facial emotion recognition after circumscribed prefrontal cortex damage

Previous studies have shown inconsistent findings regarding the contribution of the different prefrontal regions in emotion recognition. Moreover, the hemispheric lateralization hypothesis posits that the right hemisphere is dominant for processing all emotions regardless of affective valence, whereas the valence specificity hypothesis posits that the left hemisphere is specialized for processing positive emotions while the right hemisphere is specialized for negative emotions. However, recent findings suggest that the evidence for such lateralization has been less consistent. In this study, we investigated emotion recognition of fear, surprise, happiness, sadness, disgust, and anger in 30 patients with focal prefrontal cortex lesions and 30 control subjects. We also examined the impact of lesion laterality on recognition of the six basic emotions. The results showed that compared to control subjects, the frontal subgroups were impaired in recognition of three negative basic emotions of fear, sadness, and anger – regardless of the lesion laterality. Therefore, our findings did not establish that each hemisphere is specialized for processing specific emotions. Moreover, the voxel-based lesion symptom mapping analysis showed that recognition of fear, sadness, and anger draws on a partially common bilaterally distributed prefrontal network.     

Unequal impairment in the recognition of positive and negative emotions after right hemisphere lesions: a left hemisphere bias for happy faces

The processing of several important aspects of a human face was investigated in a single patient (LZ), who had a large infarct of the right hemisphere involving the parietal, and temporal lobes with extensions into the frontal region. LZ showed selective problems with recognizing emotional expressions, whereas she was flawless in recognizing gender, familiarity, and identity. She was very poor in recognizing negative facial expressions (fear, disgust, anger, sadness), but scored as well as the controls on the positive facial expression of happiness. However, in two experiments using both static and dynamic face stimuli, we showed that LZ also did not have a proper notion of what a facial expression of happiness looks like, and could not adequately apply this label. We conclude that the proper recognition of both negative and positive facial expressions relies on the right hemisphere, and that the left hemisphere produces a default state resulting in a bias towards evaluating expressions as happy. We discuss the implications of the current findings for the main models that aim to explain hemispheric specializations for processing of positive and negative emotions.     

Selective loss of complex-pitch or speech discrimination after unilateral lesion

Twenty-eight right-handed patients who suffered a single cerebrovascular accident in the distribution of either the left or right middle cerebral artery were tested on their ability to discriminate complex-pitch and speech stimuli presented dichotically. Whereas the left hemisphere lesion group was impaired in dichotic speech but not in dichotic complex-pitch discrimination, the right hemisphere lesion group was impaired in dichotic complex pitch but not in dichotic speech discrimination. Complex-pitch phenomena may provide a useful model for the study of auditory function in the nondominant hemisphere.     

Persisting apraxia in two left-handed, aphasic patients with right-hemisphere lesions

Apraxia usually follows a left hemisphere lesion in right-handers with left hemisphere speech representation. Apraxia following a right hemisphere lesion in left-handers is rare, however, and not well documented in the literature. Two left-handed patients are described in whom apraxia and aphasia followed a right hemisphere lesion. Both the apraxic and the aphasic deficits improved but were still demonstrable 6 weeks following the infarct. The data are consistent with those for right-handers with left hemisphere lesions in suggesting some overlap of anatomical structures for the control of speech and praxis.     

Drawing deficits in brain-damaged patients' freehand pictures

This study examines errors in brain-damaged patients' attempts to produce freehand drawings of common objects in response to a linguistic target (e.g., "fruit"). The pictures were carefully analyzed according to the features which dictionaries claim should vary necessarily from item to item, including color, shape, relative size, and special features which help distinguish between similar items. A "recognizability score" was created to quantify patients' overall drawing capacity. The findings revealed that subjects with right hemispheric insult are significantly more impaired overall than left hemisphere-damaged patients in producing freehand pictures. However, freehand drawing skills do not break down in an undifferentiated fashion after right hemispheric insult: Group and individual data reveal that patients with right central (primarily parietal) insult are most impaired at expressing shape attributes in their pictures, right posterior patients with primarily temporoparietal insult experience the greatest difficulty attributing color to their pictures, but patients with right anterior insult are impaired at expressing color, shape, and relative size in their pictures. All patients with right hemisphere insult often attribute specific features indiscriminantly to any member of the same category, resulting in anomalous pictures like a "potato bush." One patient with left posterior insult seemed to encounter difficulty generating the mental images necessary to serve as the basis for his pictures. These findings are discussed with reference to an image-based model for freehand drawing.     

The relationship of hemispheric preference,as measured by conjugate lateral eye movements,to accuracy of emotional facial expression

This study investigated the relationship between hemispheric preference and communication accuracy of facial affect. Hemispheric preference was determined by rating conjugate lateral eye movements. Forty right-handed females were classified: 10 right-movers (left hemisphere preference), 15 left-movers (right hemisphere preference), and 15 bidirectionals (no hemispheric preference). Subjects were shown emotionally loaded slides portraying happiness, fear, and disgust and their videotaped facial expressions were independently rated for accuracy. It was predicted that negative emotions involved right hemisphere activity and negative affect involved left hemisphere activity. As expected, it was found that left-movers were significantly better than right-movers at nonverbally communicating disgust and fear; hemispheric preference was unrelated to expression of happiness. The accuracy scores of the bidirectionals generally fell in between those of the left-movers and those of the right-movers. The results were discussed in reference to the differential lateralization of positive and negative emotions.This study was conducted as a senior research project by the first author under the supervision of the second author.     

Bilateral capacity for speech sound processing in auditory comprehension: evidence from Wada procedures

Data from lesion studies suggest that the ability to perceive speech sounds, as measured by auditory comprehension tasks, is supported by temporal lobe systems in both the left and right hemisphere. For example, patients with left temporal lobe damage and auditory comprehension deficits (i.e., Wernicke's aphasics), nonetheless comprehend isolated words better than one would expect if their speech perception system had been largely destroyed (70-80% accuracy). Further, when comprehension fails in such patients their errors are more often semantically-based, than-phonemically based. The question addressed by the present study is whether this ability of the right hemisphere to process speech sounds is a result of plastic reorganization following chronic left hemisphere damage, or whether the ability exists in undamaged language systems. We sought to test these possibilities by studying auditory comprehension in acute left versus right hemisphere deactivation during Wada procedures. A series of 20 patients undergoing clinically indicated Wada procedures were asked to listen to an auditorily presented stimulus word, and then point to its matching picture on a card that contained the target picture, a semantic foil, a phonemic foil, and an unrelated foil. This task was performed under three conditions, baseline, during left carotid injection of sodium amytal, and during right carotid injection of sodium amytal. Overall, left hemisphere injection led to a significantly higher error rate than right hemisphere injection. However, consistent with lesion work, the majority (75%) of these errors were semantic in nature. These findings suggest that auditory comprehension deficits are predominantly semantic in nature, even following acute left hemisphere disruption. This, in turn, supports the hypothesis that the right hemisphere is capable of speech sound processing in the intact brain.