H. Enger Rosvold

Localization of function within the dorsolateral prefrontal cortex of the rhesus monkey

Abstract Although lateral prefrontal lesions in the monkey are known to produce impairments on spatial delayed response and spatial delayed alternation, there is some question as to whether the delay, the spatial features, or a combination of the two is the critical factor in these tests giving rise to the impairments. Accordingly, the effects of several different lateral frontal lesions were compared on two spatial tasks, one which did involve intratrial delays (delayed alternation) and one which did not (a conditional position response test). The findings indicated the existence of two functionally distinct subdivisions of the dorsolateral prefrontal cortex: one in the principal sulcus, damage to which was responsible for impaired performance on the spatial task with delay; and the other in the arcuate sulcus, removal of which was responsible for impaired performance on the spatial task without delay. These findings together with those of other investigators suggest that the cortex in the principal sulcus may be concerned with a form of spatial memory, whereas the arcuate cortex is concerned with some other, as yet unspecified function.

Occipitotemporal corticocortical connections in the rhesus monkey

Abstract Previous behavioral studies indicated that the inferior convexity of the temporal lobe in the rhesus monkey functions in relation to the visual system and that this function probably depends on corticocortical connections which link this area to the visual areas. Therefore, in an experimental anatomical study the corticocortical connections of some of the occipital, temporal and frontal areas were investigated in the monkey, by means of the Nauta-Gygax silver impregnation technique. The following findings were obtained. The striate cortex projects to certain parts of a “circumstriate cortical belt” which extends into the caudal bank of the superior temporal sulcus in its upper parts and into the caudal parts of the intraparietal sulcus. This circumstriate belt in turn projects to the inferior convexity of the temporal lobe and to the cortex around the arcuate sulcus of the frontal lobe. The inferior convexity of the temporal lobe in turn projects back to parts of the circumstriate belt and to the lateral and the ventrolateral surface of the frontal lobe.

Projections from behaviorally-defined sectors of the prefrontal cortex to the basal ganglia, septum, and diencephalon of the monkey

Abstract Subcortical fiber degeneration in Macaca mulatta was traced by means of Nautas technique following lesions of behaviorally-defined prefrontal sectors: dorsal, principalis, lateral orbital and medial orbital. All lesions led to degeneration in parts of the anterior basal ganglia, hippocampus, medial, ventral and intralaminar thalamic nuclei, and subthalamic region. Within most of these structures, however, at least two different patterns of degeneration could be distinguished: an “orbital” pattern which differed from a “dorsolateral” one mainly in being more ventral and caudal in the basal ganglia, and more medial and denser in the thalamus and subthalamus. In addition, only orbital lesions sent fibers to the septum, or, in any substantial number, to the lateral hypothalamus. The finest differentiation among the projections was observed in the head of the caudate nucleus where each type of prefrontal lesion distributed fibers to a different locus. An attempt was made to relate the anatomical findings to behavioral studies of prefrontal-subcortical functions.

Sex-Dependent Behavioral Effects of Cerebral Cortical Lesions in the Developing Rhesus Monkey

Male rhesus monkeys with orbital prefrontal lesions were imtpaired on behavioral tests at 2� months of age whereas similar deficits were not detected in females with comparable lesions until 15 to 18 months of age. The results suggest that the maturation of a cortical region in the primate brain proceeds at different tempos in males and females.

A re-examination of the effects of frontal lesions on object alternation

Abstract Monkeys with lateral prefrontal lesions which spared the ventrolateral cortex relearned object alternation to a level of 80 per cent correct, although others with the same lesion failed to relearn spatial alternation. Neither form of alternation was relearned by monkeys with orbital removals that included the ventrolateral cortex. The results suggest that the classical delayed alternation deficit produced by an extensive prefrontal removal is compounded of two separate defects: one attributable to dorsolateral damage, and related to the spatial factor in the test; the other due to ventral damage and related to the reversal factor.

The effects of selective caudate lesions in infant and juvenile Rhesus monkeys.

Summary Monkeys given selective caudate lesions in infancy were compared with monkeys given comparable lesions as juveniles on a variety of behavioral tests beginning 10 months after surgery. The monkeys operated upon in infancy were impaired on all of the tests on which the monkeys operated upon as juveniles were impaired, and to no less degree. The results underscore the importance of the site of injury in determining future recovery from brain damage, however early in life that damage occurs. The present results obtained in monkeys with caudate lesions were also compared with previous results on the effects of prefrontal cortical injury in infancy. The finding that the early caudate lesions impair exactly those functions that the early prefrontal lesions spare, led to the conclusion that the caudate nucleus becomes functional earlier in ontogeny than the cortex and can mediate the functions that the cortex will ultimately assume.

Conditioning and extinction of a food-rewarded response after selective ablations of frontal cortex in rhesus monkeys.

Abstract Four monkeys with orbital frontal lesions, four with lateral frontal lesions, and four unoperated controls, all of which had been trained preoperatively to press a lever for food reward, were tested in conditioning sessions alternating with extinction sessions. One month later, similar conditioning and extinction tests were carried out under conditions of food deprivation and satiation. Compared to either of the other two groups, the orbital frontal animals gave more responses in extinction and showed a smaller response decrement in conditioning sessions when shifted from deprivation to satiation. These findings support the view advanced in an earlier study that the orbital frontal monkeys impairment on stimulus differentiation tests is due to a difficulty in withholding responses on negative trials. Although previous studies suggest a similar impairment in lateral frontal monkeys, the procedures used in the present experiment failed to detect it.

A comparison of the psychological test performance of patients with focal and nonfocal epilepsy

Abstract In this investigation psychological tests were used to study the performance of patients with various forms of epilepsy. A pilot study suggested that patients with temporal lobe epilepsy perform more poorly than patients with centrencephalic or diffuse epilepsy on a test of memory and that the reverse might be true on a test of attention. The memory and attention test were therefore administered to a larger, independent sample of epileptic patients which consisted of two groups with focal epilepsy (39 cases with temporal lobe and 18 with frontal lobe foci) and one group with nonfocal epilepsy (19 cases of whom 14 were of the centrencephalic variety). The several groups were matched by statistical means to control for differences in intelligence, age, duration of illness, seizure frequency, and amount of EEG abnormality. When analyzed in this manner, the results support the preliminary finding that the nonfocal (centrencephalic) patients perform more poorly than the focal patients on the test of attention; there were, however, no significant differences among groups on the memory test. Possible reasons for the inconsistent results on the memory test are discussed. The impairment of the nonfocal (centrencephalic) patient on the attention test is interpreted in terms of the Penfield and Jasper hypothesis of subcortical dysfunction in this disease.

Delayed alternation in monkeys after removal of the hippocampus

Abstract Sixteen monkeys were tested on spatial delayed alternation following complete removal of the hippocampus. Eight were trained preoperatively while eight received training only postoperatively. The results indicate that the effects of hippocampectomy on delayed alternation are extremely variable. In some instances there is relatively little impairment; in others there is severe impairment. Individual differences appear to be an important factor in determining the severity of the impairment. Some of the possible sources of these individual differences are discussed.

Topographic projections on the globus pallidus and the substantia nigra of selectively placed lesions in the precommissural caudate nucleus and putamen in the monkey

Abstract Fiber degeneration in Macaca mulatta from lesions placed selectively in the dorsal or the ventral sectors of the precommissural caudate nucleus and putamen was traced by means of the Nauta silver impregnation method as modified by Fink and Heimer. Degenerated fibers were traced from the caudate nucleus through the internal capsule to the globus pallidus where they terminated in its dorsal aspect. The fibers from the putamen were traced directly into the pallidum where they terminated in its ventral aspect. Fibers from the dorsal sector of the caudate nucleus or the putamen accumulated more laterally in the pallidum than did the fibers from the ventral sectors. There was also an anterior-posterior pattern to the termination of the fibers in the pallidum depending on the anterior-posterior location of the lesions. The only other structure in which fiber degeneration was noted was the rostral portion of the pars reticularis of the substantia nigra. The lesions in the caudate nucleus were placed in sectors defined by their afferent projections from the prefrontal cortex. Since these sectors are known to subserve the behavioral functions characteristic of the area of prefrontal cortex from which they receive afferents, the differential efferent projection emanating from the caudate probably represents a continuation of the two functional systems which originate in the prefrontal cortex.