Hemispheric mechanisms controlling voluntary and spontaneous facial expressions.

The capacity of each disconnected cerebral hemisphere to control a variety of facial postures was examined in three split-brain patients. The dynamics of facial posturing were analyzed in 30-msec optical disc frames that were generated off videotape recordings of each patient's response to lateralized stimuli. The results revealed that commands presented to the left hemisphere effecting postures of the lower facial muscles showed a marked asymmetry, with the right side of the face sometimes responding up to 180 msec before the left side of the face. Commands presented to the right hemisphere elicited a response only if the posture involved moving the upper facial muscles. Spontaneous postures filmed during free conversation were symmetrical. The results suggest that while either hemisphere can generate spontaneous facial expressions only the left hemisphere is efficient at generating voluntaly expressions. This contrasts sharply with the fact that both hemispheres can carry out a wide variety of other voluntary movements with the hand and foot.

Speech without conscious awareness.

Following commissurotomy, it is usually the case that information presented to the left hemisphere can be named and described, while information presented to the mute, right hemisphere cannot be spoken about. In the present study, it was discovered that under special test conditions, an MRI-verified, callosally sectioned adult could name or write about information presented to the right hemisphere. Studies revealed this was not an instance of right hemisphere expression. Rather, the right hemisphere was somehow able to program the left hemisphere for a spoken or written response. Further, the studies also showed that the left hemisphere was not consciously aware that it possessed the information transmitted to it by the right half brain.

Profiles of right hemisphere language and speech following brain bisection.

A variety of language tasks were administered to two patients who had undergone staged callosal section in an effort to control otherwise intractable epilepsy. Right hemisphere lexical capacity varied and preliminary results suggest that the case displaying greater semantic power also possessed some syntactic competence. This same case (V.P.) was also capable of expressive language from the right hemisphere. This rare capacity allowed for fresh observations on the dynamic interactions of conscious control that occur in this kind of patient.

Dissociation of language and cognition. A psychological profile of two disconnected right hemispheres.

Two split-brain patients who differ in their right hemisphere language capacity were tested on a variety of simple cognitive tasks. Both isolated right hemispheres performed poorly on most tests. The results suggest that the presence of language in the right hemisphere, a brain system that ordinarily does not possess such competence, need not necessarily confer the full complement of cognitive skills associated with the language processing skills of the left hemisphere.

Facial recognition and brain asymmetries: clues to underlying mechanisms.

A series of similar faces was presented to either the left or right visual field of three adults with brains surgically split along the corpus callosum. The left hemisphere displayed a marked and persistent deficit in performing a match-to-sample task, whereas the right hemisphere performed the task well. Additional test results suggest that the superiority is not specific to faces and is also not caused by specialized differences in sensory processes, but rather is related to differences in each hemisphere's ability to encode stimuli that cannot be adequately differentiated with a verbal description.

Left hemisphere visual processes in a case of right hemisphere symptomatology. Implications for theories of cerebral lateralization.

A patient with a visuospatial disturbance characteristic of posterior right hemisphere disease was examined under different conditions of stimulus presentation. The visuospatial defect, which was shown by the failure to perceive abnormalities concerning the left side of objects and the misperception of spatial relations, was present under conditions of unrestricted visual exposure. However, when the stimulus material was briefly exposed in the right visual field, performance improved substantially. These data suggest that the visuospatial defect seen after right hemisphere disease is atributable to factors other than the incapacity of the left hemisphere to process visuospatial information. Our observations, together with other evidence, lead us to question those theories of cerebral lateralization based on the notion that visuospatial processing is special to the right hemisphere.

Plasticity in speech organization following commissurotomy.

For three-and-a-half years we have been studying the cognitive and conscious mechanisms in a remarkable 18-year-old man: Case P.S. This unique individual had his corpus callosum divided in order to control intractable epilepsy. Although for some time after the operation he appeared like other split-brain patients, unable to describe verbally stimuli directed to his mute right hemisphere, he behaved as if he was capable of comprehending a wide range of language-related stimuli directed to that hemisphere. Spelling by choosing the appropriate letters with his left hand, he could process nouns, verbs, rhymes, antonyms, and superordinate concepts. When asked about tachistoscopic presentations delivered to his left visual field, he either said he had seen nothing, or only a flash of light. He was also unable to identify verbally tactile 'sterognostic' inputs to his left hand. In the last year P.S. has begun to speak about stimuli directed to his right hemisphere. This series of experiments suggests that this speech is not interhemispheric transfer within the visual modality. Further, plotting the relative increased proficiency of verbal description of inputs directed to the right hemisphere, this speech system seems to be in a process of continuing development.

Movement-dependent and movement-independent changes in hippocampal RSA in cats.

EEG was recorded from the dorsal hippocampus of cats during walking in situations intended to elicit a minimum of orienting or attentional behavior. The situations included walking in an alley for food after prolonged overtraining, and ad lib walking in an observation chamber after 24 hours habituation. In virtually all (82-100%) cases of sustained walking RSA was present in the dorsal hippocampus; however, the amplitude of the RSA during walking was quite variable and in many cases quite small. The results suggest that in the cat motoric factors may influence the occurrence of RSA and non-motoric factors may influence the amplitude of RSA.