Robert Thompson

Localization of the “maze memory system” in the white rat

Adult albino rats, previously trained on a three-cul maze, sustained bilateral cortical or subcortical lesions and were subsequently tested for retention. Those animals showing defective retention suffered damage to either the anterior neocortex, posterior neocortex, cingulate cortex, corpus striatum, hippocampus, septofornix area, thalamus (anterior, lateral, ventromedial, or posterior divisions), posterolateral hypothalamus, mamillary bodies, subthalamus, red nucleus, substantia nigra, central tegmentum, ventral portions of the brainstem reticular formation, or the cerebellum. Excellent retention was observed following damage to either the amygdaloid complex, rostral medial forebrain bundle, dorsomedial thalamus, or dorsal midbrain. These results, coupled with earlier findings, suggest that the maze habit is dependent upon the activities of three functional blocks of the brain: the first block (brainstem reticular formation) has integrative functions, the second block (sensorimotor cortex, cingulate cortex, cerebellum, and thalamus) has kinesthetic functions, and the third block (occipital cortex, hippocampus, septofornix area, and mamillary bodies) plays a role in the discrimination of spatial cues.

Near-perfect runs as a learning criterion

Abstract A new analysis is presented of a special type of learning criterion: a sequence of correct responses marred by the inclusion of at most one incorrect response. The new technique allows a significant extension of existing tables for the use of this criterion.

Localization of a “passive avoidance memory system”in the white rat

Adult rats, previously trained to refrain from entering a small dark compartment from a large illuminated compartment, sustained lesions to 1 of 53 different brain sites and were subsequently tested for retention. Retention losses were associated with lesions to the neocortex, most elements of the limbic forebrain and basal ganglia, medial portions of the thalamus and hypothalamus, colliculi, median raphe, and cerebellum. Most of these structures were also found to be critical for retention of an active avoidance habit. It was hypothesized that avoidance habits depend upon the activities of four functional blocks of the brain: the first block (basal ganglia) is concerned with sensorimotor integration, the second block (dorsal midbrain, posterior thalamus, amygdala, nucleus accumbens, and frontal cortex) plays a role in fear-initiated responses, the third block (cerebellum, anterior and ventromedial thalamus, and parietal cortex) has somatosensory functions, and the fourth block (occipital cortex, hippocampal complex, and mamillary bodies) is involved with cognitive mapping. These functional blocks require the engagement of an inhibitory mechanism (medial hypothalamus and median raphe) or an excitatory mechanism (brainstem reticular formation and anterior cingulate cortex) in order to support passive and active avoidance habits, respectively.

Stereotaxic mapping of brainstem areas critical for memory of visual discrimination habits in the rat

An attempt was made to map those pathways of the brain that are necessary for the performance of visual discrimination habits. This was accomplished by damaging different parts of the brain in previously trained rats and subsequently testing for retention. The map was constructed by plotting those areas of the brain damaged in rats showing a serious loss in retention. The resulting map could be separated into a specific (visual) division consisting of the lateral geniculate nuclei, occipital cortex, and lateral half of the cerebral peduncle at nigral levels, and a nonspecific division. Clearly represented within the latter were the ascending fiber systems associated with both the brainstem reticular formation and the substantia nigra.

The ’manipulative response memory system’in the white rat

Adult albino rats, previously trained on a series of three latch box problems, sustained bilateral cortical or subcortical lesions and were subsequently tested for retention. Those animals showing defective retention of all three problems suffered damage to either the sensorimotor cortex, corpus striatum, posterior thalamus, subthalamus, red nucleus, or brainstem reticular formation. Excellent retention of at least two of the three problems was found in animals suffering extensive occipital, cingulate, pyriform, hippocampal, septal, amygdaloid, pretectal, or tectal damage. These findings provide additional evidence for a localized cortico-subcortical system mediating learned responses in the rodent.

Thalamic regions critical for retention of skilled movements in the rat

Adult albino rats, previously trained on two latch-box tasks, sustained discrete bilateral thalamic or cortical lesions and were subsequently tested for retention. Significant deficits on the most difficult task were associated with damage to the anterior, dorsomedial, ventromedial, ventrolateral, basolateral, parafascicular, and posterior portions of the thalamus; the pretectum; and the frontal, parietal, and anterior cingulate regions of the cortical surface. These results, coupled with earlier findings on latch-box, maze, and discrimination habits, suggest that learned manipulative acts are dependent upon the activities of three functional blocks of the brain: The first block (brainstem reticular formation and basal ganglia) may have integrative functions; the second block (parietal and anterior cingulate regions; anterior, ventromedial, ventrolateral, and basolateral thalamic areas; and cerebellum) has nonvisual sensory discrimination functions; and the third block (frontal cortex and dorsomedial thalamus) plays a role in somatosensory regulation of the distal musculature.

Localization of the “incline plane discrimination memory system” in the white rat

Blinded rats, previously trained to choose an upward sloping pathway and to avoid a downward sloping pathway (a vestibulo-kinesthetic discrimination problem), sustained bilateral cortical or subcortical lesions, and were subsequently tested for retention. Those animals earning zero or negative savings scores suffered damage to either the parietal cortex, cingulate cortex, corpus striatum, septofornix area, entopeduncular nucleus, posterolateral hypothalamus, anterior, ventromedial, lateral-ventral, or posterior thalamic nuclei, subthalamus, brainstem reticular formation, medial longitudinal fasciculus, red nucleus, ventral tegmental area, substantia nigra, interpedunculo-central tegmental area, or cerebellum. These results, coupled with earlier findings on the maze and visual discrimination habits, suggest that the incline plane habit is dependent upon the activities of three functional blocks of the brain: the first block (brainstem reticular formation and associated nuclei) has arousal and integrative functions, the second block (parietal cortex, cingulate cortex, septofornix area, thalamus, and cerebellum) has functions related to the construction and utilization of a nonvisual “cognitive map,” and the third block (vestibular system) plays a role in spatial discrimination involving up vs. down.

Hypothalamic structures critical for the performance of a locomotor escape response in the rat.

Abstract Rats previously trained to avoid foot-shock by crossing a grid floor showed a relatively permanent loss of both the avoidance and escape response following bilateral damage to the far-lateral hypothalamic area and the medial tip of the cerebral peduncle. The evidence suggests that this deficit results from the abolishment of the ‘affective’ component normally elicited by noxious stimuli.

Brainstem reticular formation lesions: Amnestic effects on learned habits in the rat

Adult albino rats, previously overtrained on a brightness and a pattern discrimination habit, sustained bilateral lesions to the brainstem reticular formation and were subsequently tested for retention. Those groups receiving lesions to the basolateral mesencephalic reticular formation or to the paramedial portion of the reticular formation at either the dimesencephalic juncture, mes-metencephalic juncture, or rostral pontine levels exhibited significant losses in retention of the pattern habit. Lesions destroying either the dorsomedial mesencephalic reticular formation or brainstem areas dorsal, lateral, or ventral to the reticular formation failed to produce significant retention deficits on either habit. Similar findings were obtained in connection with the retention of a nonvisual (kinesthetic) discrimination habit.

RETROACTIVE EFFECT OF INTERPOLATED VISUAL STIMULATION

In a previous study, Thompson and Bryanr (8) showed that the interpolation of maximal light stimulation has a detrimental effect on the memory of a visual discrimination habit. Two groups of rats were given training on a horizontal-vertical discrimination problem after which one group was immediately placed in a dark room for 48 hr., while the other group was kept in a lighted room for a corresponding interval. Better retention scores were obtained in the group receiving minimal visual stimulation. These results were explained in terms of differential neural activity within the striate cortex where in rats the memory traces for visual habits appear to be localized. The present experiment attempted to determine which one of the two main theories of retroactive inhibition more adequately accounts for these data. According to the perseveration theory (5, lo), the interpolation of maximal visual stimulation might be conceived as partially depressing perseverative activity after original learning. This decrement in the perseverative process would lead to a reduction in the fixation or consolidation of the memory trace. According to a transfer theory (cf. 3), on the other hand, the opportunity for new visual learning would be present in the group kept in the lighted room. These newly formed visual habits acquired during the interpolated period would cause retroactive inhibition through competition among responses resulting from similarity between the original learning and the interpolated learning. Specifically, the present study involved the interpolation of light stimulation at varying periods after the completion of training on a visual discrimination problem. On the basis of a perseveration theory, interference would be maximal if light stimulation were introduced immediately after training. This prediction, however, does not follow from a transfer theory which makes no assumptions about a perseverative process.