Michael S. Gazzaniga

The Cognitive Neurosciences

Ed Michael S Gazzaniga MIT Press, pounds sterling64.95, pp 1447 ISBN 0 262 07157 6 The performance artist Laurie Anderson referred to her fathers death as being “like a library burning to the ground.” If the higher functions of human beings make up such a collection of texts then we are perhaps approaching some knowledge of their titles. More especially we are cognisant of the complexity that we face: an evolved network of interrelated systems capable of dynamic change; the coding of experience—memory; prefrontal systems which release us from the constraints of the immediate present, allowing us to reflect upon time future, past, and hypothetical; maps of cerebral activity which alter and adjust to the …

Forty-five years of split-brain research and still going strong

Forty-five years ago, Roger Sperry, Joseph Bogen and I embarked on what are now known as the modern split-brain studies. These experiments opened up new frontiers in brain research and gave rise to much of what we know about hemispheric specialization and integration. The latest developments in split-brain research build on the groundwork laid by those early studies. Split-brain methodology, on its own and in conjunction with neuroimaging, has yielded insights into the remarkable regional specificity of the corpus callosum as well as into the integrative role of the callosum in the perception of causality and in our perception of an integrated sense of self.

Handbook of Cognitive Neuroscience

representation and a role mapping that representation into a less abstract representation of what we actually say, as represented in (26): (26) bu sh + plural ca p + plural ca b + plural abstract

MANIPULO-SPATIAL ASPECTS OF CEREBRAL LATERALIZATION: CLUES TO THE ORIGIN OF LATERALIZATION

The right hemisphere advantage for split-brain patients on a variety of spatial tasks (block design, cube drawing, wire figures, and fragemented stimuli) is found to be highly dependent upon the involvement of manual activities in the perception of spatial relationships or the production of spatial responses. The cerebral localization of the neural substrate of manipulo-spatial functions suggests why the hemispheres differ along the manipulo-spatial dimension. These observations, in conjunction with other clinical data, are suggestive of the origins of cerebral lateralization.

Language and speech capacity of the right hemisphere

Abstract Right hemisphere language and speech capacity was further analyzed in brain-bisected patients. The results indicate that little or no syntactic capability exists in the right hemisphere. The only semantic dimension that was comprehended in a series of pictorial-verbal matching tests was the affirmative-negative. Moreover, earlier indications of a right hemisphere speech capacity could not be confirmed. Differences in verbal reaction time to visual stimuli projected to right and left hemispheres were alternatively interpreted as consequences of subcortical transfer mechanisms or cross-cuing strategies.

Dissociation of Spatial and Temporal Coupling in the Bimanual Movements of Callosotomy Patients

The neural mechanisms of limb coordination were investigated by testing callosotomy patients and normal control subjects on bimanual movements Normal subjects produced deviations in the trajectories when spatial demands for the two hands were different, despite temporal synchrony in the onset of bimanual movements Callosotomy patients did not produce spatial deviations, although their hands moved with normal temporal synchrony Normal subjects but not callosotomy patients exhibited large increases in planning and execution time for movements with different spatial demands for the two hands relative to movements with identical spatial demands for the two hands This neural dissociation indicates that spatial interference in movements results from callosal connections, whereas temporal synchrony in movement onset does not rely on the corpus callosum

Understanding complexity in the human brain

Although the ultimate aim of neuroscientific enquiry is to gain an understanding of the brain and how its workings relate to the mind, the majority of current efforts are largely focused on small questions using increasingly detailed data. However, it might be possible to successfully address the larger question of mind-brain mechanisms if the cumulative findings from these neuroscientific studies are coupled with complementary approaches from physics and philosophy. The brain, we argue, can be understood as a complex system or network, in which mental states emerge from the interaction between multiple physical and functional levels. Achieving further conceptual progress will crucially depend on broad-scale discussions regarding the properties of cognition and the tools that are currently available or must be developed in order to study mind-brain mechanisms.

Selective Activation of a Parietofrontal Circuit during Implicitly Imagined Prehension

It is generally held that motor imagery is the internal simulation of movements involving ones own body in the absence of overt execution. Consistent with this hypothesis, results from numerous functional neuroimaging studies indicate that motor imagery activates a large variety of motor-related brain regions. However, it is unclear precisely which of these areas are involved in motor imagery per se as opposed to other planning processes that do not involve movement simulation. In an attempt to resolve this issue, we employed event-related fMRI to separate activations related to hand preparation-a task component that does not demand imagining movements-from grip selection-a component previously shown to require the internal simulation of reaching movements. Our results show that in contrast to preparation of overt actions, preparation of either hand for covert movement simulation activates a large network of motor-related areas located primarily within the left cerebral and right cerebellar hemispheres. By contrast, imagined grip selection activates a distinct parietofrontal circuit that includes the bilateral dorsal premotor cortex, contralateral intraparietal sulcus, and right superior parietal lobule. Because these areas are highly consistent with the frontoparietal reach circuit identified in monkeys, we conclude that motor imagery involves action-specific motor representations computed in parietofrontal circuits.

Coding Strategies and Cerebral Laterality Effects

In a short-term recognition memory task, Ss were given relational imagery and rehearsal coding strategies in different sessions, with probes presented to the left or right cerebral hemisphere. Consistent with a model of separate processing systems for verbally and visually coded information, Ss yielded significantly faster response latencies for probes to the left hemisphere than the right when employing the rehearsal strategy, and significantly faster latencies for probes to the right hemisphere than the left when using the imagery code. This suggests that cerebral lateral@ effects are functionally related to coding strategies, and argues for the inclusion of imagery, or generated visual information, as part of the visual processing system. As such, generated visual information may be viewed as a coding alternative to verbal mediation. It is well-known that information can be represented or coded in different forms in memory. Conrad ( 1964) noted that Ss made acoustic confusions in a recall task, even though the original stimulus presentation was visual. The acoustic confusions suggest that the Ss recoded the stimuli from a visual to a verbal base prior to recall. Posner, Boies, Eichelman, and Taylor (1969) present data which are consistent with the hypothesis that Ss can generate a visual representation of an auditorily presented letter. Further, Bahrick and Boucher ( 1968) have demonstrated that object drawings may be visually or verbally coded in memory independently. Additional research has shown that stimulus (Tversky, 1969) and task (Frost, 1972) expectancy can influence the

Mike or me? Self-recognition in a split-brain patient.

A split-brain patient (epileptic individual whose corpus callosum had been severed to minimize the spread of seizure activity) was asked to recognize morphed facial stimuli—presented separately to each hemisphere—as either himself or a familiar other. Both hemispheres were capable of face recognition, but the left hemisphere showed a recognition bias for self and the right hemisphere a bias for familiar others. These findings suggest a possible dissociation between self-recognition and more generalized face processing within the human brain.