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The eighteenth meeting of this Symposium was held at Constanz (West Germany) from June 25-29 1973. The local organizer was Pr. K. POECK (Aachen).
Restitution of function following cerebral lesions (Director: M. PIERCY)
In discussion of this paper, Professor Teuber pointed out that comparable results had been obtained by Schneider in hamsters.
Dr. N. BUTTERS (Boston) reported a series of experiments comparing deficits resulting from one-stage and serial removals of prefrontal association cortex in monkeys. Although sparing occurred following serial removal of the dorsal lateral frontal region. serial ablation of the lateral orbital cortex did not lead to an attenuation of the behavioural deficits associated with one-stage removal of this area. Although these findings appeared superficially parallel to the results from early lesion studies, there appeared to be some important distinctions between the two types of recovery. While recovery after early lesions seemed to depend upon intact subcortical structures (e.g. the caudate nucleus), recovery after serial frontal lesions in more mature animals appeared to involve cortical mechanisms. Present evidence implicates the cortex immediately adjacent to a serially ablated focus as well as more distant anterior and posterior association areas as mediators of recovery. Recovery after serial lesions also appeared to be negatively related to the amount of damage produced by each operation rather than positively related to the time interval between operations. Dr. G. ETTLINGER (London) placed emphasis on various factors additional to those discussed by Dr. Butters, e.g. on the use of behavioural strategies for circumventing deficit and on the comparative course of recovery following cortical and white matter lesions. These points were discussed in the context of the disorder of reaching which is known to follow parietal ablations in the monkey. A cine-film was shown of the progressive recovery of accuracy in reaching by a monkey with such a cortical removal. The disorder was regarded as possibly analogous to that observed in neonatal monkeys lacking opportunity for making eye-hand co-ordinated movements. Certain differences between the organisation of such co-ordination in man and monkey were also pointed out. Dr. J. OXBURY (Oxford) described research in progress on the course of recovery from right hemisphere strokes. Patients were assessed neurologically in the acute stage and neurologically and psychologically 3 weeks and 6 months after occurrence of the stroke. Cognitive status at these times was related to the presence of motor and visual deficits and compared with a control group with brain stem lesions and also with patients with left hemisphere stroke. Outcome at 6 months for right hemisphere patients with visual and motor deficits was significantly inferior to the right hemisphere group with motor deficits only. At 3 weeks right hemisphere patients with both types of deficit were impaired on a wider range of non-verbal tests than were a comparable group of left hemisphere patients. It was also noted among the right hemisphere group that, whereas some test performances showed marked improvement between 3 weeks and 6 months on at least one test there was no obvious improvement (in the group with both motor and visual defects). Dr. Oxbury drew attention to the observation that in the right hemisphere group left-sided neglect was a prominent and severe disability which tended to be specific to the material to which attention was given rather than to position in the visual field. Between 3 weeks and 6 months, left-sided neglect tends to be reduced both in severity and in the range of tasks on which neglect occurs, at least for those-patients with both motor and visual defects. The possibility was discussed that comparable right-sided neglect in the left hemisphere group might be masked as a consequence of severely aphasic patients not being tested. Dr. J. McFIE (London) was concerned with somewhat longer term recovery following non-progressive localised lesions in 68 adult patients. They were tested at 3 different intervals up to 8 yr following the lesion on sub-tests of the Wechsler Intelligence scale and on tests of verbal and visual memory. It was noted that for each lesion group at the earliest interval studied (under 1 yr) the patterns of disability resembled those already reported for acute lesions. However in the groups studied at longer intervals following the lesion, there was a clear tendency for these patterns to become less pronounced, so that the mean scores tended to approximate to the average. A similar tendency was observed on memory tests but this was much less marked for impaired verbal memory than visual memory. Dr. McFie concluded that, following a non- progressive localised lesion, there is a tendency towards re-distribution of intellectual functions so that variations become less marked. He suggested that this process might continue for as long as 8 years after the lesion. Professor R. W. SPERRY (Pasadena) made a further contribution relating to the cognitive status of patients who have undergone cerebral commissurotomy. A cine-film was shown illustrating the range of response which was possible to lateralised stimuli and attention was drawn to the level of functional improvement which could be obtained at least among the youngest patients. In addition a new technique was reported using a scleral contact lens which allowed prolonged exposure and ocular scanning of lateralised visual input. Recordings were analysed for instructed manual selection and associated emotional responses to affect-laden stimuli inserted among neutral items in visual stimulus arrays. Professor Sperry pointed out that reactions obtained from the minor hemisphere provided evidence of conscious, cognitive and emotional processes comparable to those of the major hemisphere. Dr. B. MILNER (Montreal) reported studies which followed for more than 5 yr the cognitive status of patients undergoing localised surgical removals of cortical tissue. Measured I.Q. tended to fall after 3 weeks but was generally higher than pre-operatively at long-term follow-up. However the more restricted deficits associated with focal lesions did not show a comparable course of recovery. Thus left temporal patients were still impaired on delayed recall of verbal material at long-term follow-up and right but not left temporals were still impaired in their memory for an abstract design. Similarly, at long-term follow-up left frontals were worse than left temporals on tests of word fluency. In general Dr. Milner placed emphasis on the relative lack of restitution of function with respect to the selective deficits associated with at least some focal lesions. Dr. F. NEWCOMBE (Oxford) described a longitudinal study of the course of spontaneous recovery from dyslexia in one case of left posterior cerebral abscess and two cases of head injury. Two main issues were discussed which could affect the design of any future retraining programmes. (1) The changing pattern of errors during recovery and its relationship to taxonomies of linguistic performance. (2) Quantitative aspects of recovery. Dr. Newcombe drew attention to the observation that, despite marked variation in severity of disability and the duration of recovery, there was a general tendency for restitution of function to occur asymptotically. Dr. L. VIGNOLO (Trieste) reported a study of the effects of a programme of re-education on the course of recovery from severe aphasia. Patients receiving re-education were matched with others not receiving re-education (for fortuitous reasons) and recovery of speech was studied in relation to time since lesion, type of aphasia (fluent or non-fluent) and presence or absence of re-education over a period of 6 months. It was shown that re-education has a significant positive effect on the outcome but that this effect is not dependent on the type of aphasia. Evidence was also reported to suggest that, although both the passage of time and the presence of re-education positively affect speech performance, these effects do not interact but operate independently. Professor H.-L. TEUBER (Cambridge, Mass.) opened the general discussion of this topic and also reported a follow-up study of the effects of missile wounds to the brain. Like Dr. Milner, he tended to stress the relative non-restitution of function associated with certain focal cerebral lesions and, for example, pointed out that, even after a 20 yr interval, retrograde amnesia and post-traumatic amnesia remain correlated and are also related to performance on the Army General Classification Test and the Hidden Figures Test. He pointed out however that some aspects of recovery from missile wounds were age-related. Thus, over time, those aged under 21 regained more quadrants of an initial field defect than those aged over 25. In discussing general aspects of restitution of function, he underlined 5 general problems which appeared to emerge from the papers presented. (1) Does recovery represent the restitution of the original function or is there substitution of other functions serving a similar end? (2) Which functions tend to recover and which do not? (3) Does the occurrence of recovery relate to the locus of the lesion? In this context it was suggested that bilateral lesions and lesions involving white matter might produce disproportionate deficits. (4) In what way are the prospects of recovery affected by the time course of the lesion, e.g. single stage compared with serial lesions? (5) What is the role in recovery of the recession of diaschisis? These questions provided the basis for the ensuing general discussion of mechanisms involved in recovery
Non-verbal disorders and aphasia (Director: K. POECK)
Central programming and afferent control in coordinating movement (Director: R. HELD)
For the centrally-programmed response, the role of the eliciting stimulus becomes more that of releaser, in the sense of the ethologist, than of an invariant cause of response. Research then becomes focused upon the manner in which movements elicited by stimuli originating in the world become and remain adaptive under various types of perturbations including atypical rearing conditions, artificial rearrangements, and various lesions of the central nervous system. The 6 speakers of this symposium addressed themselves to problems of sensorimotor coordination defined in this sense.
EMILIO BIZZI reported on the interrelation between head and eye movement that he and his colleagues have been studying for several years (BIZZI, KALIL, MORASSO and TAGLIASCO, 1972). Working with the rhesus monkey, they find that upon presentation of a visible target in an unpredictable position (to the monkey), the initial response is a saccadic eye movement of a magnitude approaching the angular distance of the target from the fovea, followed with very short latency (tens of msec) by a head movement. Clearly if the head movement carried the eye with it, the direction of gaze would greatly overshoot the target. However, as Bizzi and his colleagues have shown, the inception of head movement elicits the vestibulo-ocular reflex with short enough latency so as to compensate effectively for the potential overshoot. This finely adapted strategy obtains, however, only for unpredictable targets. A different strategy is adopted for pursued targets thereby providing one indication, among others, of the alternative central programs available for even these relatively simple tasks.
As further evidence of alternative strategies in the interrelation between eye and head movement. JOHANNES DICHGANS reported on the consequences of vestibulectomy in the above mentioned preparation studied by himself and Emilio Bizzi (DICHGANS, BIZZI, MORASSO and TAGLASCO. 1975). He showed that in the absence of the vestibular-ocular reflex an alternative mechanism utilizing 'proprioception from the neck may substitute to some extent. Even with neck proprioception eliminated by rhizotomy of the cervical dorsal roots, a certain amount of compensation may be achieved by substitute mechanisms which reprogram concomitant head and eye movements.
MARC JEANNEROD reported his findings on adaptation of hand tracking to optical rearrangement in which the tracking movements of the hand are displayed rotated in the frontal place by a small angle. High degrees of adaptation were found after short periods of exposure to the transformed feedback. These properties make the procedure an efficient one for the analysis of the conditions for adaptation as well as for use as a clinical tool.
Adaptation to rearrangement of the type reported by Jeannerod represents a re-calibration of the interface between incoming information about the spatial locus of the arm and hand and the motor programs controlling reach. Suspecting that the original calibration of this interface occurs during the earliest acquisition of reaching by similar exposure, RICHARD HELD and his collaborators have precluded sight of the hands and limbs during the early rearing of neonatal monkeys in order to test this notion (HELD and BAUER, 1975). Both rearing and testing of the animals were carried out under conditions in which sight of the limbs was prevented. Reaching for a visible target in one direction was operantly conditioned following which training, generalization of the reach to other directions and to use of the contralateral hand was tested. The results showed that the monkeys deprived of sight of their limbs from birth were clearly deficient relative to control animals in both learning to reach and in generalizing the direction of response once acquired. Moreover, they showed deficiencies in tactually-controlled manipulation of the target of the reach. The deprived animals develop a groping strategy of reach, not unlike that of blind animals, in response to their deficiencies. This alternative strategy is another evidence of the plasticity of behavioral control mechanisms.
JACQUES PAILLARD discussed a typology of spatially-organized movements useful for segmenting the control problem into manageable parts. As an example of such a control system, he chose to consider eye-hand coordination in the split-brain monkey. The effect of such a split including optic chiasm is to cut all cerebral commissures that may carry information relating visual target position gained by one hemisphere to control centers for arm movement in the other hemisphere. Since arm movement is controlled by the contralateral hemisphere, it is the ipsilateral combination of eye and hand which has been the subject of considerable investigation and controversy. Paillard's results suggest that use of the ipsilateral eye-hand combination in the split-brain animal is deficient, relative to the contralateral, with regard to accuracy of ballistic target-directed movement, a result somewhat at variance with Kuypers's claim that is visually controlled manipulation that is deficient.
BRUNO PREILOWSKY discussed work performed in collaboration with ROGER SPERRY on patients in whom the frontal cerebral commissures had been sectioned for relief of spreading epileptic seizures. Information crossing in these frontal commissures is more concerned with motor than sensory function. Consequently, an attempt was made to assess the deficit with the use of a task demanding synchronous activity of the two hands. On this task, the split commissure patients showed a deficiency relative to the performance of a control group of unoperated subjects.
M. PIERCY, K. POECK and R. HELD