Gregor W. Jason

Manual sequence learning after focal cortical lesions

Patients with unilateral frontal or temporal excisions and normal control subjects learned sequences of hand positions. Left-frontal and left-temporal lesions impaired learning these sequences. No group had particular trouble when order of response was restricted to the original order, compared to when it was not restricted; nor were group differences seen when subjects learned new orders of already-familiar positions. Delayed recall of the positions (which had been learned to a common criterion), was not impaired in any group. Results suggested a role of the left-frontal and left-temporal lobes in learning series of manual responses.

Performance of manual copying tasks after focal cortical lesions.

Patients with unilateral frontal or temporal excisions and normal control subjects were required (1) to copy single, difficult positions of the arm, fingers, or both, and (2) to copy the experimenter as three hand positions were presented one after the other at an increasing rate. All patient groups were impaired relative to the control group on both tasks, but on the second task patients with frontal lesions were also impaired relative to those with temporal lesions. Results suggested a role of the left-and right-frontal lobes in rapid execution of multiple manual responses.

Postischemic therapy with MK-801 (dizocilpine) in a primate model of transient focal brain ischemia

The purpose of this study was to develop a primate model for assessing EEG, behavior and histology, and to test the effect of NMDA receptor blockade in transient focal ischemia. Squirrel monkeys (Saimiri sciureus) under halothane anesthesia were subjected to 110 min of transient focal ischemia (n = 15) by temporary clip occlusion of the MCA. An eight-lead EEG was recorded. Neurobehavioral testing was done in a subgroup of animals (n = 6). Brain temperature (37.5 degrees C) was monitored and controlled to avoid hypothermia or intergroup temperature differences, and blood pressure was regulated to 60 mmHg. The entire brain was subserially sectioned, and 52 standardized coronal sections encompassing the infarct were examined histologically 2 wk after the ischemia. Animals were randomized to receive either (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine (MK-801) 1 mg/kg of maleate salt or carrier solution, 20 min and again at 12 h after the onset of ischemia. Cingulate and retrosplenial cortex were examined for NMDA-antagonist-induced neuronal necrosis. No reduction, or trend toward reduction of neurobehavioral deficit was seen with MK-801. MCA occulsion reduced EEG power over the ischemic hemisphere. MK-801 appeared to cause brain activation, and globally increased power at several frequencies. MK-801 did not reduce infarction in either neocortex (p > 0.05) or striatum (p > 0.05). No selective neuronal necrosis was seen in the cingulate or retrosplenial cortex. We conclude that MK-801 given 20 min after the onset of transient ischemia offers no significant neuroprotective effect against either neurobehavioral deficit or ischemic infarction in this model of transient focal ischemia. Further experiments in unanesthetized animals are necessary to determine if MK-801-induced necrosis exists in the gyrencephalic brain, but the enhancement of primate brain electrical activity by MK-801 suggests that brain activation occurs in primates as it does in rodents.

Acute Effects on Neuropsychological Function and Quality of Life by High‐Dose Multiple Daily Fractionated Radiotherapy for Malignant Astrocytomas: Assessing the Tolerability of a New Radiotherapy Regimen

Cognitive and other quality of life measures were assessed in 29 patients with supratentorial malignant astrocytomas before and after high‐dose (8000 cGy) multiple daily fractionated radiotherapy. Assessments were done immediately before and after radiotherapy. Patients completed a neuropsychological evaluation and the Functional Living Index: Cancer (FLIC). Spouses completed the Family Environment Scale and the Profile of Mood States. Cognitive abilities generally improved over the course of radiotherapy. Occasionally, deterioration of potential clinical importance was observed on functions associated with the tumour site. Quality of life as assessed by the FLIC was stable in most cases and improved in five, but deteriorated in three patients. Families showed slightly less Conflict and slightly more Cohesion than the norm; this was especially so when patients had greater cognitive deficit. Emotional state of spouses was variable, with increased fatigue or reduced activity most commonly reported, followed by depression and anxiety. Mostly this improved with time or remained stable, but two spouses reported worsening emotional state. Results are generally encouraging for tolerance of this radiotherapy protocol, although they demonstrate that limited adverse effects may occur in some cases.

Failure of Metacontrol: Breakdown in Behavioural Unity After Lesion of the Corpus Callosum and Inferomedial Frontal Lobes

A right-handed man suffered aneurysmal haemorrhage with lesions of the genu and body of the corpus callosum and the inferomedial frontal lobes bilaterally (right more than left). He exhibited remarkable breakdown in behavioural unity characterized by conflict between the two sides of the body, actions inconsistent with verbalizations, and internal conflict over control of the left hand. A major feature of the deficit was its temporal variability. This is interpreted as reflecting intermittent failure of metacontrol processes, which are neural mechanisms for maintaining behavioural unity. Medial frontal structures and their interconnections through the corpus callosum appear particularly important in the maintenance of metacontrol.

Fimbria-fornix lesions and sexual-social behavior of the guinea pig.

Male and female guinea pigs were given fimbria-fornix lesions and their sexual-social activity was compared to lesioned control animals. The lesions reduced the sexual and aggressive behavior of the male guinea pig. In the female, on the other hand, aggression towards the male increased during attempted copulation. Both experimental and control animals were given an open-field activity test. It was found that fimbria-fornix lesioned animals displayed less activity than did their control counterparts. These results were consistent with earlier findings and were related to previous observations of decorticate rats. It was suggested that the hippocampal output via the fimbria-fornix during sexual-social behavior plays a role in selecting motor patterns appropriate for the motivational state of the animal.

Chapter 5 Disorders of Motor Function Following Cortical Lesions: Review and Theoretical Considerations

Cerebral cortical mechanisms for limb praxis are reviewed, with an emphasis on lesion studies of humans and monkeys. There are multiple components in the cortical control of motor behavior. Prefrontal cortex is important for the direction of behavior when environmental demands are somewhat ambiguous. There are bifrontal and contralateral frontal and parietal mechanisms for the execution and exact control of movements. Premotor cortex and the supplementary motor area each appear to be involved in movement coordination as well as in the selection of movements. There is also a system for the bihemispheric integration of behavior, which involves at least the supplementary motor area and corpus callosum. In humans, there are left-hemispheric processes for the generation of specific movements from memory. Evidence supports the view that the human and monkey brain are organized very similarly, although published research has not addressed the issue of hemispheric specialization for motor tasks in the monkey.