Psychobiology

Levere, T. E.

doi: 10.3758/bf03337462pmid: N/A

Abstract The present discussion assumes that recovery of function is not an event but rather a process. When it occurs, this process bridges the gap between the occurrence of the brain injury and the reinstatement of a particular behavior disrupted by the brain injury. Accordingly, to understand the process of recovery of function, one must first appreciate the point from which the process begins, that is, the behavioral deficit. It is the thesis of the present discussion that one effect of neural injury is to cause the individual to shift behavioral control to neural systems not directly affected by the neurological insult. The behavioral deficit is then the result of the individual’s attempting to learn new behaviors to compensate for those normally mediated by the damaged neural system. Recovery of function, on the other hand, represents a return to the neural system directly affected by the injury and the utilization of whatever of this system may be spared.

Thompson, Robert;Hale, David B.;Bernard, Bryan A.

doi: 10.3758/bf03337463pmid: N/A

Abstract Rats previously trained on a successive brightness discrimination—go left in the presence of two black cards and go right in the presence of two white cards—sustained bilateral lesions to one of nine brain regions (parietal cortex, anterior cingulate cortex, posterior cingulate cortex, cerebellum, anterior thalamus, ventromedial thalamus, ventrolateral thalamus, lateral thalamus, and ventrobasal thalamus) thought to be concerned with the maintenance of habits having a proprioceptive-kinesthetic basis. The retention test disclosed that each of the nine brain-damaged groups showed significant deficits in the performance of the successive problem. Damage to the motor cortex, hippocampus, septofornix, or medial longitudinal fasciculus also led to significant retention deficits, but mammillary body or mediodorsal thalamic lesions had no effect. These findings suggest that left-right differentiation has a proprioceptive-kinesthetic basis in addition to a possible vestibular basis.

Moore, John W.;Stickney, Kenneth J.

doi: 10.3758/bf03337464pmid: N/A

Markowitsch, Hans J.;Guldin, Wolfgang;Kessler, Josef;Riess, Rudolf

doi: 10.3758/bf03337465pmid: N/A

Abstract Running activity of guinea pigs was compared before and after ablation of the cortical projection areas of the medial and lateral sectors of the thalamic mediodorsal nucleus (sulcal vs. medial prefrontal cortex). Only ablation of the sulcal prefrontal cortex was followed by a significant increase in running activity. This result corresponds to similar observations made in another rodent species, the rat, and also made in nonrodent species. Therefore, it is concluded that, with respect to basic or unlearned functions, interspecies parallels can be drawn for the cortical projection area of the medial portion of the mediodorsal nucleus. At the same time, it is, however, emphasized that the prefrontal cortex cannot be considered to be structurally and/or functionally homogeneous among species.

Weis, Bonita J.;Means, Larry W.

doi: 10.3758/bf03337466pmid: N/A

Abstract Two experiments were conducted to investigate the hypothesis that the medial frontal cortex and dorsomedial thalamus constitute a neural system mediating a common set of behaviors. Rats with bilateral medial frontal lesions, unilateral medial frontal lesions, bilateral medial thalamic lesions, unilateral medial thalamic lesions, contralateral medial frontal and medial thalamic lesions, and sham operations were compared on spontaneous alternation and visual-tactile discrimination. Only rats with bilateral medial thalamic lesions were found to be deficient on the two tasks. Thus, while the present experiments are consistent with earlier work demonstrating that a functional medial thalamus is necessary for normal spontaneous alternation and discrimination, the present experiments failed to support the notion that the medial thalamus and medial frontal cortex constitute a common behavioral system.

Miller, S. Walden;Christensen, Janet M.

doi: 10.3758/bf03337467pmid: N/A

Abstract One of the difficulties encountered in attempts to underestand the process of recovery following damage of the septal nuclei is that a variety of disorders are produced by the damage and that not all seem to recover at similar rates. It has been suggested that environmental conditions influence recovery such that rates may be either increased or attenuated. In the present study, the passive avoidance deficit that follows lesion of the medial septal nuclei in rats was observed for periods of 20 and 70 days. The damage produced marked passive avoidance deficits that were observed at 20 days but not at 70 days. Although lesion subjects rapidly acquired the passive avoidance response at 70 days, their learning patterns were unlike those of control subjects, suggesting acquisition via different neural substrates. Moreover, tests for retention of the passive avoidance task revealed retention deficits in all lesion subjects. Two groups of subjects were allowed to recover for 70 days, one housed in a high-stimulus environment and the other in a low-stimulus environment. Effects of environment on recovery from lesions were not detected. However, comparisons of normally housed subjects with those housed in the high- and low-stimulus environments showed that the low-stimulus environment produced passive avoidance deficits primarily in control subjects. The findings are discussed within a framework of specific and nonspecific arousal.

Modaresi, Heidar A.;Hart, Robert P.;Nenja, Leonard H.

doi: 10.3758/bf03337468pmid: N/A

Abstract Two experiments were conducted to assess the hypothesis that septal lesions result in a decrement in conditioned fear and to investigate whether the different effects of septal lesions in one-way and two-way avoidance tasks are due to some procedural differences between these two tasks. Experiment 1 compared the septal and normal control rats in a two-way avoidance task that incorporated a safe platform under the subject after a response but did not involve handling the subject (one-way analogue task). Experiment 2 investigated the effects of septal lesions in conventional two-way and one-way analogue tasks with two levels of shock intensity. The results indicated that, in the absence of a moving partition or electrified grids on top of the hurdle, the one-way analogue task enhanced the performance of both the normals and septals with both levels of shock intensity. Shock intensity had no effect in the one-way analogue task, but the more intense shock degraded the performance of both septals and normals in the two-way task. These results are not predicted by the fear-attenuation hypothesis. An alternative hypothesis in terms of the septals’ deficiency in the utilization of spatial cues was tested and shown able to account for all of the present results.

Ison, James R.;Reiter, Levi A.

doi: 10.3758/bf03337469pmid: N/A

Abstract In Experiment 1, the amplitude of the acoustic startle reflex in rats was shown to increase linearly with increases in the intensity of the eliciting stimulus (Se). A preliminary stimulus (Si), a light flash, inhibited the reflex. The amplitude of the reflex was reduced by an equal amount regardless of Se intensity. In Experiment 2, the amplitude of the same reflex was shown to have a biphasic relation to the intensity of a white noise background (Sn) and reflex amplitudes peaked at the intermediate noise levels. Although the vigor of the reflex elicited in the presence of the most intense noise approximated that elicited by the weak Se in Experiment 1, in this condition the reflex was unaffected by the occurrence of the otherwise inhibitory light flash. It has been previously hypothesized that the decrement in reflex vigor obtained at high Sn results because sensory masking of Se by Sn reduces the effective intensity of Se. The different effect of Si in these two conditions suggests that this hypothesis is incorrect. A hypothetical neural model was devised to account for the difference between the two reflexes in their susceptibility to a preliminary stimulus, and the model was extended to other effects of stimulus strength and background noise on reflexive behavior.

Warren, J. M.

doi: 10.3758/bf03337470pmid: N/A

Abstract A survey of the developmental, genetic, paleoneurological, comparative behavior, and neuropsychological evidence indicates that the neural organization responsible for handedness and laterality in humans is a heritable, species-specific trait. Handedness and laterality in monkeys, the most intensively studied nonhuman taxon, are not homologous to handedness and laterality in humans. Monkeys learn hand preferences through experience and display no difference in learning by the hemispheres ipsi- and contralateral to the preferred hand. Differences in the functions of the two hemispheres are found in several other nonhuman species, but none has been correlated with paw preferences.

Siegfried, Bert;Bureš, Jan

doi: 10.3758/bf03337471pmid: N/A

Abstract Unilateral 6-hydroxydopamine (6-OHDA) injections into the nigrostriatal system of rats were used to interfere with a lateralized reaching-for-food habit, the so-called “handedness.” Experiment 1: Although injections of 6-OHDA into the substantia nigra (8 µg/4 µl) ipsilateral (n=7) to the preferred forelimb had no effect on the overlearned instrumental reaction, reaching was blocked 15 min after contralateral (n=12) injection of the neurotoxin and remained suppressed for the 8 days of testing. At the same time, retrieval of food with the nonpreferred forepaw significantly increased. Although the rats failed to reach into the feeder, behaviors like grasping, grooming, or holding food pellets were intact in the “neglected” forepaw. Nonspecific effects such as changes in activity level or motivation could be ruled out by the ipsilateral-contralateral test paradigm used. The early behavioral asymmetries (blockade of handedness, flexion of the forelimb, and ipsilateral turning) are interpreted as due to interference of 6-OHDA with membrane structures of dopaminergic neurons. Experiment 2: Injections of 6-OHDA into the caudate nucleus contralateral (30 µg/5 µl, n=9) to the performing forelimb initially blocked handedness similarly as in Experiment 1. However, in contrast to nigral injections, reaching recovered within 6 days. Experiment 3: One month after a unilateral 6-OHDA lesion of substantia nigra, naive rats (n=7) acquired the reaching-for-food habit with the paw ipsilateral to the lesion. It is concluded that the blockade of handedness produced by unilateral 6-OHDA lesions of substantia nigra is not due to paralysis of the forelimb but to faulty integration of the contralateral somatosensory signals with contralateral motor patterns.