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Many investigations have been conducted in an effort to deduce the nature of hippocampal function. This paper is an overview of the work done by several researchers in their attempt to find the possible connections between overt behaviors and hippocampal structures in the rat.
The mutant no-bridge (nobKS49) has its name from a structural defect in the protocerebral bridge of the central complex. This rod-shaped neuropil in nobKS49 has a large gap at the sagittal midplane, with some of the missing material accumulated more laterally. Mutant nob flies have a reduced maximal and average walking speed. Leg coordination is disturbed during turning but not while walking straight. Motivation for walking is low and steps are small due to slow forward swinging of the legs. Flies spontaneously may pass into an autistic (and possibly spastic) state in which they can move their legs and even perform cleaning movements but do not walk or fly. They spontaneously recover if left undisturbed. Gynandromorph experiments place the focus of the walking defects into the head. Mutant flies have a reduced tendency to escape when mechanically stimulated. In a brightly lit arena they do not avoid a black square above the horizon and they are negatively phototactic. In tethered flight optomotor responses are normal but the amplitude of spontaneous torque modulations as well as the number of torque spikes are reduced. If a single black bar is slowly rotated around the fly, the normal response pattern is observed. It vanishes, however, at moderately fast angular velocity at which the wild type still is fully responsible. The behavioral defects support the notion that the protocerebral bridge is part of a higher center for the regulation of behavior.
Rats explore objects by rhythmically whisking them with their mystacial vibrissae. On two types of tactile discrimination tasks, macrogeometric and microgeometric, better performers palpated the discrimnanda for longer periods of time and used movement patterns that appeared to optimize whisking frequency bandwidth and the extent to which the vibrissae would be bent by object contact. On a task involving finely textured surfaces, good and poor performers differed in the temporal components of their whisking patterns, whereas the spatial domain was more important for animals palpating surfaces with widely separated features. These findings are consistent with increasing neurophysiological evidence that the central representation of the tactile periphery, in rodents and other mammals, is both integrative and dynamic.
The relationship of measures of sensation seeking and trait anxiety to drug use and reasons for drug use was studied among a sample of 92 detained or adjudicated adolescent males in a residential detention facility. Experience seeking was found to be related to drug use in general, and especially use of "hard" drugs. Anxiety tended to be related to drug avoidance, except in the case of marijuana and alcohol use. Reasons for drug use which related with experience seeking were excitement and thrill oriented, whereas reasons associated with anxiety were related to feelings of discomfort for this sample. In general, experience seeking was a stronger factor than trait anxiety in these findings. Implications for more action-oriented and less insight-oriented treatment are discussed in light of these results.
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One purpose of the two studies reported here was to examine the reactions of rats to changes in the spatial arrangement of a familiarized environment under low stress conditions. The second purpose was to test the role of rats' experience with novelty. In Experiment I the novelty was manipulated by introducing new tunnels into one zone of the experimental chamber. The introduction of novelty took place after 11 habituation sessions. In Experiment II in the course of habituation sessions the experimental group of rats was subjected to a persistent change of tunnel arrangement in the experimental zone, whereas for the control group nothing changed. All animals reacted to the novelty with increased time spent in the experimental zone and decreased time spent in other zones. Both experiments show that under low stress conditions rats demonstrate a positive response toward novelty and that their previous experience with novelty does not affect that reaction.
Open field activity was studied in Wistar rats. Animals with low scores of ambulatory and rearing behaviours were grouped as hypoactive and those with high scores as hyperactive. Acquisition of active avoidance learning in a shuttle box was studied in the two groups. Hyperactive rats in contrast to hypoactive rats showed a better acquisition of avoidance learning. Learning was suppressed in both groups by domperidone, but was facilitated by immobilisation stress in the hypoactive group only. The two groups did not differ in the basal and stress evoked heart rates. These observations suggest that immobilisation stress favours enhancement of the dopaminergic related behaviour like avoidance learning in hypoactive rats.
The septal nuclei are reciprocally connected with the hippocampal formation and contribute importantly to spatial and memory processing. Using excitotoxic lesions of the septal area, we investigated whether neurodegeneration in subcortical projections to hippocampus can compromise flexible information processing by hippocampal single units. In agreement with the mild effects of excitotoxic septal lesions on hippocampal physiology compared with fimbria-fornix lesions and septal inactivation, we observed limited lesion effects on single-unit activity. The location specificity of hippocampal complex spike cells remained unchanged, but a less reliable location-dependent discharge was observed in experimental animals with a pronounced postoperative working memory deficit. Testing in the absence of ambient illumination and in a new environment revealed that the spatial correlates of complex spike cells in lesioned animals may rely on a more limited set of sensory cues. Altered sensory cues resulted in a significantly different response pattern between the control and lesion group in the new environment, a situation that normally results in place field reorganization. Such a group difference was not observed during dark testing, a condition in which place field reorganization is less prominent. A contribution of hippocampal interneurons to the observed alterations in the spatial properties of the principal cells was suggested by decreased theta modulation in the lesioned group. Because excitotoxic lesions result in memory deficits that resemble age-related memory problems in the absence of age-related degenerative processes, we suggest that septal neurodegeneration could directly contribute to those behavioral changes with advanced age that correlate with functional alterations in the hippocampal formation.
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The perirhinal cortex appears to play a key role in memory, and the neighboring hippocampus is critically involved in spatial processing. The possibility exists, therefore, that perirhinal-hippocampal interactions are important for spatial memory processes. The purpose of the present study was to investigate the contribution of the perirhinal cortex to the location-specific firing ("place field") of hippocampal complex-spike ("place") cells. The firing characteristics of dorsal CA1 place cells were examined in rats with bilateral ibotenic acid lesions centered on the perirhinal cortex (n = 4) or control surgeries (n = 5) as they foraged in a rectangular environment. The activity of individual place cells was also monitored after a delay period of either 2 min, or 1 or 24 hr, during which time the animal was removed from the environment. Although the perirhinal cortex lesion did not affect the place field size or place cell firing characteristics during a recording session, it was determined that the location of the place field shifted position across the delay period in 36% (10 of 28) of the cells recorded from lesioned animals. In contrast, none of the place cells (0 of 29) recorded from control animals were unstable by this measure. These data indicate that although the initial formation of place fields in the hippocampus is not dependent on perirhinal cortex, the maintenance of this stability over time is disrupted by perirhinal lesions. This instability may represent an erroneous "re-mapping" of the environment and suggests a role for the perirhinal cortex in spatial memory processing.
Searching activity (SA) is the way to satisfy the need of overcoming and the mechanism of development of all forms of behavior under conditions of deficit of pragmatic information. SA is temporarily incorporated into the structure of the initial phase of all behavioral forms. The SA has energy and cognitive components that can be measured using Grigoriev's technique and his problem box. Quantitative and qualitative characteristics of SA are of prior significance in the structure of appetitive behavior and minimal significance in the structure of drinking behavior. Under described experimental conditions, in the structure of defensive behavior the values of the SA indices are mean.
A clear relationship exists between moment-to-moment behavioral elements and hippocampal rhythmical synchronous activity (RSA) (theta rhythm). However, behavioral elements are not isolated events but are part of behavioral sequences in a context of behavioral activity. By concurrently monitoring open field behavior and hippocampal EEG, EEG correlates of open field behavior in relation to preceding and following behavior were studied in Sprague Dawley rats to determine whether the behavioral context influences EEG correlates of behavior. Results show that preceding and subsequent behavioral patterns influenced the spectral power correlates of behavior. RSA power was increased when a "type 1 behavior" (voluntary movement) preceded the behavior compared with when a "type 2 behavior" (automatic movement, awake immobility) preceded it. The modulating effect of behavioral transitions was shown for several types of behaviors, and systematic modulation of hippocampal EEG correlates of behavior was demonstrated. The present report shows that the strong and systematic relationship between hippocampal RSA and behavior is modulated by the behavioral-sequential context. Thus, in addition to the well established relationship between RSA and motor activity, a second nonmotor process seems to contribute to hippocampal RSA. A likely candidate is a sensory process, which is in accordance with theories on the sensorimotor function of hippocampal RSA.
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No linear differences in the corticosterone basal levels or in its changes following weak stress effects were revealed in rats with active (KHA) or passive (KLA) behavioural strategy. A strong immobilisation stress alone was able to evoke significant linear differences in the hypophyseal-adrenocortical system's responsiveness. The hormonal response to stress was prolonged in the KHA rats as the increased level of corticosterone in the blood of these animals was longer preserved than in the KLA rats. The results suggest both a different sensitivity of the hypophyseal-adrenocortical system and a different velocity of the stress response deactivation in active and in passive animals.
After a 6-week social isolation (from 22nd to 70th day from birth) male Wistar rats (a sibship, 10 animals), were tested for 20 min in a light/dark box in order to reveal behavioral features of choice of their spatial localization in unknown conditions. Socially deprived rats significantly differed from control animals in longer time of the room choice, higher number of entries of the light section, and higher number of rearings, which was probably explained by their higher anxiety and lack of experience to estimate unexpected stimuli and select a response. The mean level of behavioral activity during exploration of the box defined by the number of elementary operations per minute remained constant and was significantly higher in the socially deprived rats than in the control animals.
In the past, it has been proposed that the rat vibrissae play an important role in other hand, postural abnormalities, muscle tone decreases and hypomotility after sensory organ destructions were proposed as evidence supporting the "level setting" or "tonic" hypothesis. This hypothesis postulates that afferent activity, besides its well know transductive functions, sets the excitability state of the central nervous system. We thought the vibrissal system to be a good model to dissect these two postulated roles because vibrissae trimming would annul the transductive function without affecting the integrity of nerve activity. Thus we compare the effects of trimming the whiskers with blocking the vibrissal afferent nerves on two types of motor behavior: activity in an open field and walking over a rope connecting two elevated platforms. We found that only vibrissal afferent blockage (both nerve section and local anaesthesia) produced severe failures in the motor performances studied. These effects could not be fully explained by the abolition of the vibrissae as a sensory modality because cutting the whiskers did not significantly affect the motor performance. These data are discussed in reference to a tonic or general excitatory function of sensory inputs upon the central nervous system.
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The effects of massive lesions of the telencephalon on the behavioral repertoire of captive pigeons were investigated. The behavior of four birds with an intact telencephalon was compared to that of four birds submitted to ablation of telencephalic structures. Behavioral audio recording was done according to previously defined categories in three daily sessions for fifteen days. Experimental birds were followed up for one month. Immediately after the lesion, operated birds showed decreases in the occurrence of different behaviors such as coordinated movements, feeding, interaction, preening, maintenance, exploration and vocalization and increases in locomotion and discrete movements of the body when compared to the control birds (P less than 0.05). Recovery of exploration (P less than 0.05), feeding and localization was observed during the follow-up period. These data are interpreted as suggestive of a functional role of the telencephalon in the organization of behavior and a long-term recovery of behavior after detelencephalation.