R. W. Sperry

Preferential selection of central pathways by regenerating optic fibers.

Abstract The time-course and general features of optic nerve regeneration in goldfish were followed in sections prepared at spaced intervals between 3 and 67 days after nerve section. Differential route and destination preferences of fibers from different parts of the retina were then tested by removing specific portions of the retina in combination with complete section of the optic nerve. With the dorsal half of the retina destroyed, surviving ventral fibers became segregated beyond the nerve scar and selectively entered the medial tract to connect with dorsal tectum. Conversely, when dorsal retina remained intact, the regenerating fibers filled selectively the lateral tract and the ventral tectum. Fibers from the posterior (temporal) hemiretina invaded the anterior portion of the tectum and did not extend into the posterior regions. Conversely, those from the anterior hemiretina bypassed the anterior zones to innervate the posterior tectum. Fibers from the center of the retina, after reaching the parallel layer within the tectum, bypassed the plexiform layer in the margin to connect only in the central zone. The plexiform layer in the marginal zones was innervated only when fibers were available from the peripheral retina. The results furnish direct microscopical evidence for the orderly selective termination of optic fibers in the brain centers. They also demonstrate a remarkable and unexpected (presumably chemotactic) selectivity in the tendency of different retinal fiber groups to choose and to follow specific central pathways en route to their synaptic destinations. The thesis that specific chemical affinities govern the formation and maintenance of neuronal associations is extended on the basis of the present results to include the patterning of central fiber pathways.

Lateralized suppression of dichotically presented digits after commissural section in man.

Right-handed patients with surgical disconnection of the cerebral hemispheres cannot report verbal input to the left ear if diferent verbal stimuli have been channeled simultaneously to the right ear. With monaural stimulation, they show equal accuracy of report for the two ears. These findings highlight the dominance of the contralateral over the ipsilateral auditory projection system. Suppression of right-ear input is obtained in nonverbal tests. Dissociation between verbal and left-hand stereognostic responses indicate a right-left dichotomy for auditory experience in the disconnected hemispheres.

Self recognition and social awareness in the deconnected minor hemisphere.

Abstract 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 subjects 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.

Mind-brain interaction: Mentalism, yes; dualism, no

Abstract A traditional working hypothesis in neuroscience holds that a complete account of brain function is possible, in principle, in strictly neurophysiological terms without invoking conscious or mental agents; the neural correlates of subjective experience are conceived to exert causal influence but not mental qualities per se . This long established materialist-behaviorist principle has been challenged in recent years by the introduction of a modified concept of the mind-brain relation in which consciousness is conceived to be emergent and causal. Psychophysical interaction is explained in terms of the emergence in nesting brain hierarchies of high order, functionally derived, mental properties that interact by laws and principles different from, and not reducible to those of neurophysiology. Reciprocal upward and downward, interlevel determination of the mental and neural action is accounted for on these terms without violating the principles of scientific explanation and without reducing the qualities of inner experience to those of physiology. Interaction of mind and brain becomes not only conceivable and scientifically tenable, but more plausible in some respects than were the older parallelist and identity views of the materialist position. This revised concept of consciousness as causal, with its recognition of mental phenomena as explanatory constructs in science, has brought a marked change during the past decade in the scientific status of consciousness and of mental and cognitive phenomena generally. Resultant mehtalist trends within science have been accompanied also by a corollary rise in acceptance of various mentalist-related concepts and dualist beliefs in the supernatural, the paranormal and in unembodied forms of conscious existence that receive no logical support from the new mind-brain concepts of neuroscience. Reasons are advanced to show that our latest mind-brain model is fundamentally monistic and not only fails to support dualism, but serves to further discount fading prospects for finding dualist forms or domains of conscious experience not embodied in a functioning brain.

Some long-term motor effects of cerebral commissurotomy in man ☆

Abstract The long-term effects of cerebral commissurotomy on motor co-ordination and dyspraxia were investigated in 8 patients who had undergone complete or partial commissurotomy 5–10 yr previously. Performance on a series of standardized motor co-ordination and manual dexterity tests was compared with the established norms. Although qualitative performance appeared essentially unimpaired on most tests the scores for speed were consistently below normal and also inferior to those reported for patients with various unilateral brain lesions. In certain bimanual tasks requiring rapid alternating motion and interdependent control severe qualitative and quantitative impairments were present. In addition, marked dysgraphia and mild ideomotor-type dyspraxia on the left side, and moderate dyscopia on the right were present up to 10 yr after surgery in patients with complete commissurotomy. It would appear from the results that interhemispheric communication becomes particularly important for motor output to the extent that the tasks involve complex intermanual coordination or hemispheric specialization with ipsilateral control.

Hemisphere lateralization for cognitive processing of geometry.

Abstract A 54-item cross-modal visuo-tactile test involving geometrical discriminations in Euclidean, affine, projective and topological space (plane and 3-dimensional) was administered to 7 subjects with commissurotomy, 2 with hemispherectomy, 1 with agenesis of corpus callosum, and to 5 normal controls. Using blind manual stereognosis subjects selected one of a choice of three shapes, screened from sight, that best fitted a set of five different geometrical forms presented together on a panel in free vision. An intuitive apprehension of geometrical relations was involved that did not require formal training in geometry. Findings support a consistent minor hemisphere superiority and disclose orderly differences in left hemisphere capabilities correlated with the different types of geometry.

The impact and promise of the cognitive revolution.

Opening a new era in science, psychologys cognitive revolution contradicts traditional doctrine that science has no use for consciousness to explain brain function. Subjective mental states as emergent interactive properties of brain activity become irreducible and indispensable for explaining conscious behavior and its evolution and get primacy in determining what a person is and does. Dualistic unembodied consciousness is excluded. A modified two-way model ofinterlevel causal determinism introduces new principles of downward holistic and subjective causation. Growing adoption in other disciplines suggests the two-way model may be replacing reductive physicalism as the basic explanatory paradigm of science. The practice, methods, and many proven potentials of science are little changed. However, the scientific worldview becomes radically revised in a new unifying vision of ourselves and the world with wide-ranging humanistic and ideologic as well as scientific implications.

Hemispheric Specialization in Nonverbal Communication

Subjects sustaining right hemisphere damage were impaired in the ability to evaluate emotional situations presented through nonverbal means, particularly through facial expressions. Left brain damage, even of considerable extent, led to significantly milder deficits. In agreement with these findings, a study in split-brain patients showed the isolated right hemisphere to be competent in evaluating facial expressions but less sensitive to body movements, while the left hemisphere showed the opposite pattern.

LATERALITY EFFECTS IN SOMESTHESIS FOLLOWING CEREBRAL COMMISSUROTOMY IN MAN

Abstract A variety of basic somatosensory tests carried out on a patient with surgical section of the cerebral commissures revealed a marked separation of somesthetic effects from right and left extremities and from right and left sides of the trunk. Predominantly contralateral projection of somesthesis was evident; the presence of any ipsilateral representation at all four regions below the neck remained questionable. Bilateral projection was indicated in results from the face and the top and back of the head with equal representation on both sides. Comparatively little functional impairment was the rule when the sensory and motor output involved the same hemisphere, but severe impairment and complete incapacity were evident when right-left cross integration was required. These and similar results in the present case suggest that in the absence of cerebral damage during infancy, transcallosal interaction is of critical importance for utilization of ipsilateral somesthetic data particularly when the left extremities participate in activities involving the symbolic functions of the dominant hemisphere.

Performance on the Raven's Colored Progressive Matrices Test by Subjects with Cerebral Commissurotomy

Summary A modified form of the Ravens Colored Progressive Matrices Test was administered to a group of patients with surgical section of the cerebral hemispheres in order to compare the independent capacity of left and right hemispheres for spatial apprehension and reasoning as indicated by this standardized test. The patterns with missing parts were presented in free vision but the answer had to be sought among a choice of three metal-etched patterns in blind tactual exploration using the left and right hands separately. Scores for the two hands as well as speed of performance showed a consistent left hand-right hemisphere superiority, even though the order of presentation was biased in favor of the left hemisphere. Scores for the left hemisphere, however, were well above chance and the results indicate that the test can be performed by either the right or left hemisphere but that the two use different strategies of approach and different , modes of central processing.