Ernest Greene

Thalamic role in spatial memory.

The contribution of structures in the limbic diencephalon to spatial memory function was investigated. Rats with lesions of either the anteroventral thalamus, anteromedial thalamus, dorsomedial thalamus or mammillary bodies were compared in their ability to perform a delayed alternation task. The results indicate the ablation of the thalamic nuclei did not impair delayed-alternation memory, but there was impairment following damage to the mammillary bodies. Placement of the discrete lesions was verified using Nissl sections and by tracing the pattern of projections using a silver degeneration stain. The results suggest that individual thalamic nuclei are not essential in the storage and/or retrieval of spatial memory. The data are discussed in terms of spatial deficits resulting from damage to the hippocampus proper or to the pathways connecting it to other brain structures.

The role of mammillary bodies in spatial memory

Abstract The role of the mammillary bodies in spatial function was investigated by testing the ability of rats to perform a single-alternation habit. Mammillary-damaged and control animals were tested under conditions which provided for a brief delay or for no delay between successive trials. Experiment 1 tested animals on acquisition of the habit; the results indicate that mammilary lesion impairs learning of the spatial alternation habit and that intertrial delay adds significantly to the dysfunction. The results of experiment 2 suggest that retention of the habit is not impaired when the lesion is inflicted after the initial learning. Both experiments suggest that the mammillary bodies are essential in the storage and/or retrieval of recent maze choices and support the position that they play a role in spatial memory. The evidence also suggests that mammillary body deterioration is responsible for the spatial confusion which characterizes humans suffering from Korsakoffs psychosis.

Behavioral role of hippocampal connections

Abstract The functions of particular afferent and efferent connections of the hippocampus were evaluated in a sequence of learning tasks. Rats with damage to the fornix were impaired in learning to reverse a position habit, learning to alternate position, learning to extinguish running for water reward, and in learning a passive avoidance habit. A lesion of the subiculum or of the cingulum produced an impairment in avoidance learning only. Exploration of an open field, learning of the original position habit, and running latencies in performing the maze habits were not significantly affected by any lesion treatment. The results of this study support the position that the hippocampus is involved in separable functions. “Response suppression” may be one of its activities, but the hippocampus also appears to have a special role in the storage and recall of spatial habits.

Behavioral role of the mammillary efferent system

The present study examined the effects of lesions of the mammillary system on spatial memory and arousal. Destruction of the medial mammillary nucleus or the mammillotegmental tract produces impairments on a delayed alternation task and greatly increases activity in the open-field. Lesions of the mammillothalamic tract produce a differential effect in that the spatial alternation deficit is accompanied by a general lethargy and unresponsiveness. It is suggested that the mammillary system plays a crucial role in the short-term storage of proprioceptive information necessary for the successive execution of maze choices. It also appears to play a role in the arousal state of the animal.

Effects of hippocampal lesion on cardiovascular, adrenocortical and behavioral response patterns in mice ☆

Abstract It was found that animals with a hippocampal lesion developed high blood pressure, low heart rates, and high plasma corticosterone during social interaction in a territorial situation. However, hippocampal animals kept in a nonterritorial situation with minimal social interaction did not show significant cardiovascular or plasma corticosterone changes as compared to unoperated controls or cortically lesioned controls. The socially interacting hippocampal animals failed to develop a social hierarchy and did not respond aggressively to an intruder placed in the colony. The data suggests that the hippocampus is involved in the maintenance of social behavior which in turn may modulate autonomic nervous system activity.

Evaluating Müller-Lyer effects using single fin-set configurations

Four experiments were conducted to study the bias of perceived length for Müller-Lyer configurations that contained a single set of fins (i.e., two segments that join to form a vertex). The experiments manipulated several factors that have been shown to be critical to the effect: (1) version (which way the apex pointed), (2) length of the stimulus span, (3) presence or absence of a line segment in the span being judged, (4) fin length, (5) fin angle, and (6) the zone in which the response was rendered. Using percent error as the index of perceptual distortion, the major finding was that the two versions show an opposite slope for strength of effect as a function of span. When stimulus spans were plotted against response means (not converting to percent error), an almost perfect linear relation was found. These results indicate that the perceptual effects can be modeled as a linear system having two parameters through which the treatments exert their influence. The results are discussed in relation to major theories of mechanism for the Müller-Lyer illusion.

Orienting bias in the rat produced by hippocampal lesion

A recent view of hippocampal function is that it acts as an attentional gating device, a theory which relies heavily on the inability of hippocampally lesioned animals to orient normally. The results of the first experiment are consistent with the attentional theory: unilateral lesions of the hippocampus produce ipsilateral orienting to symmetrically presented stimuli. However, a second experiment shows that the direction of orienting bias to a visual stimulus is not altered by cutting the optic chiasm, a procedure which functionally reverses visual influence to lesioned and intact hemispheres. Since the direction of bias produced by unilateral hippocampal lesion is unchanged by this reversal of sensory input, it seems likely that the orienting bias is due to a motor rather than a sensory impairment.

Behavioral effects of lesions of precommissural and postcommissural fornix

Lesions which sever different parts of precommissural or postcommissural fornix were compared to the effects of control lesions in several behavioral tasks. Spatial learning and avoidance was impaired by lesions of the descending columns, or by lesions which sever the precommissural communications passing to and from medial septum. Damage to precommissural fibers through lateral septum produced a measurable change only on the avoidance task. This pattern of deficits, considered together with the anatomical relationship of the system, suggests a model in which the medial septum relays kinesthetic information to dorsal hippocampus, which in turn serves as a memory system in the performance of spatial habits. It is less clear what kind of information is relayed by lateral septum, but it may communicate with ventral hippocampus regarding the consequences of punishment, and thus serve as part of a system for defensive suppression of behavior.

Minicomputer monitored social behavior of mice with hippocampus lesions.

A detailed behavioral analysis (24 hr/day) was made of four groups of socially interacting male CBA mice in a population cage during a 24-day period. The four groups were: hippocampus lesioned animals, cortical lesioned control animals, sham operated, and unoperated control animals. Each male was magnetically tagged, and individual transactions were detected using Hall Effect sensors located at the portals to each of the eight chambers in the population cage. The sensors interfaced with a minicomputer and teletype that produced 6-hr behavior profile reports for each male. The animals with hippocampus lesions exhibited significantly higher locomotor activity and patrol patterns that peaked on day 8 at a level five times that of the control groups. They also showed greater consistency of circadian activity rhythm over the 24-day period as well as greater crest-trough amplitude as compared to control groups. The animals with hippocampal lesions spent more time in the food chamber and included it more in their patrols than the control animals. Less aggression was observed in this group, and they failed to develop a social hierarchy with dominant-subordinate relationships. However, with time locomotor activity returned to normal, and increased flight responses were observed. The evidence suggests that the hippocampus may indeed be involved with the experience and control of emotion and social behavior.

The Corner Poggendorff

With the classic Poggendorff illusion a set of parallel ‘induction lines’ will cause a set of oblique line segments to look misaligned even though they are collinear. A different kind of misalignment can be produced by placing the induction lines so that they form a corner. Under these conditions the obliques will appear to be angled slightly, one relative to the other. The effects are small, but can be seen and reliably reported by a group of naive subjects. The influence of the induction lines drops sharply as their relative position is moved from parallel to orthogonal, but there is a small residual influence which may be called the corner Poggendorff effect.