Self recognition and social awareness in the deconnected minor hemisphere

Two patients with cerebral commissurotomy were tested with visual input lateralized to left or right half of the visual field by an opaque hemifield screen set in the focal plane of an optical system mounted on a scleral contact lens which allowed prolonged exposure and ocular scanning of complex visual arrays. Key personal and affect-laden stimuli along with items for assessing general social knowledgability were presented among neutral unknowns in visual arrays with 4-9 choices. Selective manual and associated emotional responses obtained from the minor hemisphere to pictures of subject's self, relatives, pets and belongings, and of public, historical and religious figures and personalities from the entertainment world revealed a characteristic social, political, personal and self-awareness comparable roughly to that of the major hemisphere of the same subject

Linguistic Competence and Related Functions in the Right Cerebral Hemisphere of Man Following Commissurotomy and Hemispherectomy

A simple new contact lens technique has been developed to permit the presentation of continuously lateralized visual information to one visual half field at a time. Free unilateral scanning of the information and monitoring of performance in the subjects' lap makes it possible to administer a variety of standard perceptual and cognitive tasks to either hemisphere in order to assess hemispheric specialization under natural conditions. Two representative commissurotomy patients have been fitted with the new device and have undergone an extensive series of language and related studies focusing on the right hemisphere. All tests were administered unilaterally to each hemisphere and subsequently in free vision. The results were correlated with data from a group of three hemispherectomy patients in two of whom the right (non dominant) and in one of whom the left (dominant) cerebral hemisphere has been surgically removed for the treatment of post infantile tumor. The case of dominant hemispherectomy is particularly rare and permits the study of language competence and performance in a girl whose language lateralization for speech and hearing was well under way (perhaps completed) when the tumor set in. Results of extensive clinical aphasia tests reveal a distinct hierarchy of language functions from a relatively good auditory comprehension through a more severe speech deficit, to almost complete alexia, agraphia and acalculia. Theoretical aphasiological analysis of the pattern of impairment in language functions here shows that in spite of characteristic nonfluency and anomia in speech, the syndrome is unique and does not correspond to either a Broca's or anomic aphasia. The agraphia and especially the alexia in this patient are more severe than in the separated right hemisphere of the two commissurotomy patients which can read a wide range of individual words and even short sentences. This is in contrast to her superior expressive speech relative to the right hemisphere of the same two commissurotomy patients. In a series of studies comparing the psycholinguistic abilities of the two hemispheres in the two commissurotomy and three hemispherectomy patients it was shown that the right cerebral hemisphere had extensive ability to elicit meaning from pictures and to recognize semantic associations and form concepts. In particular it was able to ignore perceptual for semantic similarity. Lateralized tests of visual closure reveal the conditions under which right hemisphere visual feature extraction mechanisms fail. Previous results on superior right hemisphere competence in completing patterns from fragmented information must now be qualified by the provision that when the gestalt of the visual ground is strong and in competition with the figure, the right hemisphere is unable to complete partial patterns. Neither can it recognize complete embedded figures in the face of distracting gestalt in the ground. Right hemisphere competence in various aspects of auditory language comprehension has been investigated with the aid of an experimental paradigm involving matching an auditory message to one of unilaterally presented alternative line drawings. Lower limit age estimates for right hemisphere comprehension of vocabulary were obtained and it was shown that the right hemisphere can comprehend not only abstract words but also a variety of syntactic structures including verbs, and sentential transformations and to a lesser degree long nonredundant and semantically abstract references. Right hemisphere pattern of syntactic competence has weak correlation with order of acquisition in children and somewhat stronger with aphasics. In contrast, aural vocabulary in the right hemisphere, although consistently inferior to the left, follows the same function of frequency as the left just as do children and aphasics.</p

Quantitative analysis of cortical pyramidal neurons after corpus callosotomy.

This study quantitatively explored the dendritic/spine extent of supragranular pyramidal neurons across several cortical areas in two adult male subjects who had undergone a callosotomy several decades before death. In all cortical areas, there were numerous atypical, supragranular pyramidal neurons with elongated “tap root” basilar dendrites. These atypical cells could be associated with an underlying epileptic condition and/or could represent a compensatory mechanism in response to deafferentation after callosotomy

Fast Visuomotor Processing of Redundant Targets: The Role of the Right Temporo-Parietal Junction

Parallel processing of multiple sensory stimuli is critical for efficient, successful interaction with the environment. An experimental approach to studying parallel processing in sensorimotor integration is to examine reaction times to multiple copies of the same stimulus. Reaction times to bilateral copies of light flashes are faster than to single, unilateral light flashes. These faster responses may be due to ‘statistical facilitation’ between independent processing streams engaged by the two copies of the light flash. On some trials, however, reaction times are faster than predicted by statistical facilitation. This indicates that a neural ‘coactivation’ of the two processing streams must have occurred. Here we use fMRI to investigate the neural locus of this coactivation. Subjects responded manually to the detection of unilateral light flashes presented to the left or right visual hemifield, and to the detection of bilateral light flashes. We compared the bilateral trials where subjects' reaction times exceeded the limit predicted by statistical facilitation to bilateral trials that did not exceed the limit. Activity in the right temporo-parietal junction was higher in those bilateral trials that showed coactivation than in those that did not. These results suggest the neural coactivation observed in visuomotor integration occurs at a cognitive rather than sensory or motor stage of processing

The neural correlates of social attention: automatic orienting to social and nonsocial cues

Previous evidence suggests that directional social cues (e.g., eye gaze) cause automatic shifts in attention toward gaze direction. It has been proposed that automatic attentional orienting driven by social cues (social orienting) involves a different neural network from automatic orienting driven by nonsocial cues. However, previous neuroimaging studies on social orienting have only compared gaze cues to symbolic cues, which typically engage top-down mechanisms. Therefore, we directly compared the neural activity involved in social orienting to that involved in purely automatic nonsocial orienting. Twenty participants performed a spatial cueing task consisting of social (gaze) cues and automatic nonsocial (peripheral squares) cues presented at short and long stimulus (cue-to-target) onset asynchronies (SOA), while undergoing fMRI. Behaviorally, a facilitation effect was found for both cue types at the short SOA, while an inhibitory effect (inhibition of return: IOR) was found only for nonsocial cues at the long SOA. Imaging results demonstrated that social and nonsocial cues recruited a largely overlapping fronto-parietal network. In addition, social cueing evoked greater activity in occipito-temporal regions at both SOAs, while nonsocial cueing recruited greater subcortical activity, but only for the long SOA (when IOR was found). A control experiment, including central arrow cues, confirmed that the occipito-temporal activity was at least in part due to the social nature of the cue and not simply to the location of presentation (central vs. peripheral). These results suggest an evolutionary trajectory for automatic orienting, from predominantly subcortical mechanisms for nonsocial orienting to predominantly cortical mechanisms for social orienting

Neural Basis of Self and Other Representation in Autism: An fMRI Study of Self-Face Recognition

Autism is a developmental disorder characterized by decreased interest and engagement in social interactions and by enhanced self-focus. While previous theoretical approaches to understanding autism have emphasized social impairments and altered interpersonal interactions, there is a recent shift towards understanding the nature of the representation of the self in individuals with autism spectrum disorders (ASD). Still, the neural mechanisms subserving self-representations in ASD are relatively unexplored.We used event-related fMRI to investigate brain responsiveness to images of the subjects' own face and to faces of others. Children with ASD and typically developing (TD) children viewed randomly presented digital morphs between their own face and a gender-matched other face, and made "self/other" judgments. Both groups of children activated a right premotor/prefrontal system when identifying images containing a greater percentage of the self face. However, while TD children showed activation of this system during both self- and other-processing, children with ASD only recruited this system while viewing images containing mostly their own face.This functional dissociation between the representation of self versus others points to a potential neural substrate for the characteristic self-focus and decreased social understanding exhibited by these individuals, and suggests that individuals with ASD lack the shared neural representations for self and others that TD children and adults possess and may use to understand others

Split-brain reveals separate but equal self-recognition in the two cerebral hemispheres

To assess the ability of the disconnected cerebral hemispheres to recognize images of the self, a split-brain patient (an individual who underwent complete cerebral commissurotomy to relieve intractable epilepsy) was tested using morphed self-face images presented to one visual hemifield (projecting to one hemisphere) at a time while making "self/other" judgments. The performance of the right and left hemispheres of this patient as assessed by a signal detection method was not significantly different, though a measure of bias did reveal hemispheric differences. The right and left hemispheres of this patient independently and equally possessed the ability to self-recognize, but only the right hemisphere could successfully recognize familiar others. This supports a modular concept of self-recognition and other-recognition, separately present in each cerebral hemisphere

Split-brain patients neglect left personal space during right-handed gestures

Since some patients with right hemisphere damage or with spontaneous callosal disconnection neglect the left half of space, it has been suggested that the left cerebral hemisphere predominantly attends to the right half of space. However, clinical investigations of patients having undergone surgical callosal section have not shown neglect when the hemispheres are tested separately. These observations question the validity of theoretical models that propose a left hemispheric specialisation for attending to the right half of space. The present study aims to investigate neglect and the use of space by either hand in gestural demonstrations in three split-brain patients as compared to five patients with partial callosotomy and 11 healthy subjects. Subjects were asked to demonstrate with precise gestures and without speaking the content of animated scenes with two moving objects. The results show that in the absence of primary perceptual or representational neglect, split-brain patients neglect left personal space in right-handed gestural demonstrations. Since this neglect of left personal space cannot be explained by directional or spatial akinesia, it is suggested that it originates at the conceptual level, where the spatial coordinates for right-hand gestures are planned. The present findings are at odds with the position that the separate left hemisphere possesses adequate mechanisms for acting in both halves of space and neglect results from right hemisphere suppression of this potential. Rather, the results provide support for theoretical models that consider the left hemisphere as specialised for processing the right half of space during the execution of descriptive gestures