Revisiting places passed: sensitization of exploratory activity in rats with hippocampal lesions

We examined the involvement of the hippocampus in short-term changes in exploratory behaviour in an open field (Experiment 1) and experimental contexts (Experiment 2). In Experiment 1, rats with excitotoxic lesions of the hippocampus were more likely to revisit recently visited zones within the open field than were control rats. Similarly, in Experiment 2 rats with hippocampal lesions showed greater exploration of a context that they had recently explored than a context that they had less recently explored. This short-term sensitization effect was not evident in control rats. These findings are consistent with the suggestion that the recent presentation of a stimulus has two opposing effects on behaviour, sensitization, and habituation, and that hippocampal lesions disrupt the short-term process responsible for habituation, but not that responsible for sensitization.     

Revisiting places passed: Sensitization of exploratory activity in rats with hippocampal lesions

We examined the involvement of the hippocampus in short-term changes in exploratory behaviour in an open field (Experiment 1) and experimental contexts (Experiment 2). In Experiment 1, rats with excitotoxic lesions of the hippocampus were more likely to revisit recently visited zones within the open field than were control rats. Similarly, in Experiment 2 rats with hippocampal lesions showed greater exploration of a context that they had recently explored than a context that they had less recently explored. This short-term sensitization effect was not evident in control rats. These findings are consistent with the suggestion that the recent presentation of a stimulus has two opposing effects on behaviour, sensitization, and habituation, and that hippocampal lesions disrupt the short-term process responsible for habituation, but not that responsible for sensitization.     

Genetic factors and the measurement of exploratory activity

The progenitor strains C57BL/6 and BALB/c and the seven recombinant inbred strains derived from them were used to examine the genetic relationship between two measures of activity and hippocampal lamination defect (Hld). Fifty-three mice (Mus musculus), 9 from each of the progenitor strains and 5 from each recombinant inbred strain, were tested for 16 min in a device which permitted both unobstructed traverse of the length of a runaway and contact with objects which were aligned alongside the runway. The C57BL/6 mice produced significantly more locomotor (runway traversal) activity, whereas the BALB/c showed significantly greater amounts of investigatory (object contact) activity. This reversal of relative position in the distribution of scores was not present for the recombinant strains. There was no dichotomous separation of recombinant strains for either measure. Examination of activity in terms of four consecutive 4-min periods indicates differences among the strains with respect to changes during the test session. The strains may be dichotomized with respect to decrement in activity within the 16-min session, but these groups do not correspond with those reported by others. The inference of a single genetic determinant for activity measured either as locomotor or investigatory responses is not supported by these data, nor is there any apparent relationship between activity and Hld. The critical influence of genetic-environment interactions in determining behavior and the effect of the selection of measurement techniques upon interpretation of data are emphasized by these data.     

Effects of fear on exploratory behaviour in rats

It has been suggested that mild fear may evoke rather than inhibit exploratory responses in rats. The relationship between conditioned fear and exploratory behaviour was analysed in three experiments and there was no evidence that mild fear increased exploration. Conditioned fear was found to be under relatively precise stimulus control and its magnitude was related to the intensities and durations of the unconditioned stimulus, inescapable electric shock.     

Retroaction and Gains in Motor Learning: III. Evaluation of Results

(O. S. S. STAFF. Assessment of Men. New York: Rinehart, 1948. Pp. 541.) Reviewed By Cecil A. Gibb     

Walk on the bright side: physical activity and affect in major depressive disorder

Although prescribed exercise has been found to improve affect and reduce levels of depression, we do not know how self-initiated everyday physical activity influences levels of positive affect (PA) and negative affect (NA) in depressed persons. Fifty-three individuals diagnosed with Major Depressive Disorder (MDD) and 53 never-depressed controls participated in a seven-day experience sampling study. Participants were prompted randomly eight times per day and answered questions about their physical activity and affective state. Over the week, the two groups of participants did not differ in average level of physical activity. As expected, participants with MDD reported lower average PA and higher average NA than did never-depressed controls. Both participants with MDD and controls reported higher levels of PA at prompts after physical activity than at prompts after inactive periods; moreover, for both groups of participants, PA increased from a prompt after an inactive period to a subsequent prompt at which activity was reported. Depressed participants in particular showed a dose-response effect of physical activity on affect: longer duration and/or higher intensity of physical activity increased their PA significantly more than did short duration and/or lower intensity physical activity. Physical activity did not influence NA in either group. In contrast to previous treatment studies that examined the effects of prescribed structured exercise, this investigation showed that self-initiated physical activity influences PA. These findings also underscore the importance of distinguishing between PA and NA to gain a more comprehensive understanding of the effects of physical activity on affect in MDD.     

Habituation of exploratory activity to new stimuli, to the absence of a previously presented stimulus and to new contexts, in rats

Rats trained to run a shuttle-alleyway for food exhibited exploratory behaviour to a novel visual/tactual stimulus presented in a specific place of the alley. Intermittent presentation of the same stimulus in the same place resulted in reduction of the exploratory activity (habituation), both within and between sessions. The animals also directed exploratory activity to the absence of the previously presented stimulus at the place where the stimulus had been presented before; this latter response also habituated. The presentation (1) of the same stimulus to which the animals had already habituated in another place in the alleyway or when the animals were running in an opposite direction to the previous trials of stimulus presentation, or (2) of another stimulus, resulted, again, in the appearance of exploratory activity. These results lead to the conclusion that the animals code external events, store this information, and use it to detect spatial- and directional-contextual changes and to generate predictions about that specific environment.     

Interactive effects of noise with illumination and age on activity of rats

Locomotor activity of male, albino rats (25, 90, and 200 days old at the start of the experiment) was measured in conditions of light and dark. Continuous and pulsed noises of 50, 60, 70, 80 and 90 dB were presented under each illumination condition. While noise intensity altered activity of all age groups, it interacted with illumination and age, resulting in different sensory-dependent patterns of activity in each age group. The results are interpreted in terms of arousal theory and potential functional development of CNS structures regulating the effects of ambient sensory input on behavior.     

Manual cyclical activity as an exploratory tool in neonates

Haptic texture perception was investigated in 3-day-old infants. Following a habituation sequence with a smooth or granular object, babies received a haptic test during which they held either the familiar or a new textured object. Two dependent measures were recorded: (1) Holding time was used to assess habituation as well as reaction to novelty and (2) hand pressure frequency exerted on the object was used to investigate neonates’ capacity to adjust their manipulation to the texture of objects. Both measures revealed neonates’ capacity to haptically perceive the texture of objects. From the results, it can be concluded that neonate’s manual cyclical activity recorded by HPF is a primary exploratory tool that is both necessary and sufficient to obtain knowledge about texture.