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The effect of number of trials per day during sequential alternation of unilateral amygdaloid stimulation
Abstract
Three groups of rats were subjected to a sequence of stimulations alternating from one amygdala to the contralateral one. Each phase of stimulation was for six convulsions prior to stimulation of the opposite side. Rats in Group 1 were stimulated six times per day; Group 2 rats had three trials each day; and one stimulation each day was provided for Group 3 rats. The oscillation tendency (high values for one side, low values for other side) was prominent with all groups but seemed most prevalent with Group 3 rats.
Data from a number of sequential alternation experiments were factor analyzed to determine the number of common factors present. Three dependent variables (latency of convulsion, number of trials to six convulsions, duration of convulsions) were evaluated by three procedures: principal components solution with 1s in main diagonals, principal axes solution with largest r in the diagonals, principal axes solution with R2 in the diagonals. The results were similar; the presence of two factors was suggested in the latency and criterion measures (primary site stimulation and secondary site stimulation) and one in the duration data. A principal components factor analysis over the three dependent variables showed the presence of three factors, those observed in each of the separate analyses.
In two experiments, rats were subjected to a sequence of stimulations alternating from one amygdala to the contralateral one. Each phase of stimulation was for six convulsions prior to alternation to the other side. Rats In Experiment 1 had a series of six or seven phases of alternation, followed by five phases of bilateral stimulation, and concluded with seven phases of unilateral stimulation. In Experiment 2, rats had five phases of bilateral stimulation prior to seven phases of unilateral stimulation. The bilateral phases produced a modest disruption of the oscillation tendency when it was interspersed between two series of unilateral stimulation phases, more so in the criterion measure than in latency data. The effect was less on the oscillation tendency when bilateral stimulation preceded unilateral stimulation phases.
There are three types of interference effects during kindling: that produced by alternate stimulation of homologous brain sites, by successive stimulation of one site, and by stimulation of one site by different frequencies. These three types of interference appear to be similar. Facilitation and interference effects during kindling seem to be generated by the operation of two factors: a “neurological trace” process, possibly involving synaptic changes, and an “aftereffect.” The latter process may be the main basis for these interference effects.
Previous research indicated that an oscillation effect resulted during sequential alternation of unilateral electrical stimulation of the amygdala over 10 phases of six clonic convulsions per phase, with consistent low latency values for one side and consistent high values for the contralateral one (i.e., a fluctuation of low and high values on consecutive phases). In the present experiment 10 rats were stimulated for up to 50 phases. Four of the 10 showed remarkable patterns of oscillation in latency data: One oscillated on every one of 50 phases, two showed oscillation patterns on 48 of 50 phases, and the fourth oscillated on every one of 32 phases.
Three groups of rats were subjected to a sequence of electrical stimulations alternating from one amygdala to the contralateral one. In Group 1 each stimulation was for one convulsion prior to stimulation of the opposite side. Rats in Group 2 had six convulsions per phase. Twelve convulsions per phase were provided for Group 3 rats. The oscillation tendency (high values for one side, low values for the other side) was prominent with all groups, but seemed less prevalent for the rats in the one convulsion per phase group.
Fifteen rats showing prominent oscillation patterns in latency during sequential alternation of unilateral amygdaloid stimulation were separated into three groups of five rats each. Group 1 rats were rested for 1 month prior to continuing sequential alternations. Groups 2 and 3 rats were rested for 3 months and 6 months, respectively. In spite of these rest intervals, most rats continued to show the same oscillation pattern as that before the rest period.
Previous experiments using a sequence of alternating unilateral stimulations of the amygdalae indicated an “oscillation effect”, i.e., consistent low-latency values for convulsions elicited from one amygdala and consistent high-latency values for convulsions elicited by stimulation of the contralateral amygdala. The present study was concerned mainly with statistical evaluations of the reliability of oscillation events. Tests of the randomness of the observed primary and secondary oscillation patterns indicated that oscillation patterns were significant systematic ones in latency, criterion, and duration data, with the greatest frequency of oscillation occurring in the latency measure. Although there was no significant difference in the frequency of primary or secondary oscillation using chi-square methods, an analysis of variance trend analysis indicated that the primary oscillation pattern (low values on primary side) was the predominant one when considered over the total sample, 139 rats. Also, it was shown that the behavioral pattern (oscillation, nonoscillation) appears not to be related to the number of trials to reach the criterion of six convulsions. The exact basis for oscillatory behavior is unknown. However, for a number of reasons, it appears to be based probably on transfer and interference effects between the primary and secondary brain sites.
Previous research had indicated that an oscillation effect resulted during sequential alternation of unilateral amygdaloid stimulation with consistently low latency values for one side and consistently high values for the contralateral one. The effect of intensities approximately 15 microA above threshold was investigated in this study. The oscillation tendency occurred at these near-threshold intensities both for rats which previously had shown oscillation patterns at different intensities and for those which were being stimulated for the first time.
Previous research with the kindling paradigm indicated that an oscillation effect resulted during sequential alternation of unilateral amygdaloid stimulation with consistently low values for one side and consistently high values for the contralateral one. The effect of interphase intervals of 1 and 14 days following (Experiment 1) and during (Experiment 2) the development of oscillation was investigated in this study. In Experiment 1 both the 1-day and 14-day intervals disrupted the oscillation tendency in criterion data but not in the latency measure. In Experiment 2 disruption of oscillation occurred only for the criterion measure in the 14-day group.
Previous research indicated that sequential alternation of stimulation of certain homologous brain areas via chronically implanted electrodes resulted in oscillation of high and low latencies for convulsions. This phenomenon suggested the establishement of interhemispheric facilitatory-inhibitory effects as a result of repeated stimulation of the two brain sites. In the present study, the latency oscillation pattern was observed in split-brain rats as well as in bilaterally stimulated controls, but not in rats stimulated on one side only. Significant differences were observed between split-brain and control rats in terms of initial kindling rates, duration of convulsions and type of oscillation. Results are discussed in the context of possible interhemispheric mechanisms involved in long term kindling.
In two experiments, rats were subjected to a sequence of stimulations alternating from one amygdala to the contralateral one. Each phase of stimulation was for six convulsions prior to alternation to the other side. Rats In Experiment 1 had a series of six or seven phases of alternation, followed by five phases of bilateral stimulation, and concluded with seven phases of unilateral stimulation. In Experiment 2, rats had five phases of bilateral stimulation prior to seven phases of unilateral stimulation. The bilateral phases produced a modest disruption of the oscillation tendency when it was interspersed between two series of unilateral stimulation phases, more so in the criterion measure than in latency data. The effect was less on the oscillation tendency when bilateral stimulation preceded unilateral stimulation phases.
In two experiments, rats were subjected to a sequence of electrical stimulations alternating from one amygdala to the contralateral one. Each phase of stimulation was for six convulsions prior to alternation to the other side. An oscillation effect resulted, involving low trials to six clonic convulsions and low latency to convulse for stimulation of one side, but high values of these measures for the contralateral site. The oscillation persisted, especially for the latency measure, even when one phase of bilateral stimulation preceded unilateral stimulation, when a 17- to 23-day rest period was inserted following a sequence of alternations and when two phases of bilateral stimulation occurred following postrest unilateral stimulations. The oscillation effect was less prominent in the number of trials to six convulsions data and almost nonexistent in duration of convulsion. Of 16 rats used in 15 to 19 alternating phases, 7 oscillated throughout all of these phases in latency data, but none showed oscillation over all phases in the other dependent variables.
Brief bursts of nonpolarizing electrical brain stimulation were presented once each day at constant intensity. At first the stimulation had little effect on behavior and did not cause electrographic afterdischarge. With repetition the response to stimulation progressively changed to include localized seizure discharge, behavioral automatisms and, eventually, bilateral clonic convulsions. Thereafter, the animal responded to each daily burst of stimulation with a complete convulsion. The effect was obtained from bipolar stimulation of loci associated with the limbic system, but not from stimulation of many other regions of the brain. Parametric studies and control observations revealed that the effect was due to electrical activation and not to tissue damage, poison, edema, or gliosis. The changes in brain function were shown to be both permanent and trans-synaptic in nature. Massed-trial stimulation, with short inter-burst intervals, rarely led to convulsions. The number of stimulation trials necessary to elicit the first convulsion decreased as the interval between trials approached 24 hours. Further increase in the inter-trial interval had little effect on the number of trials to first convulsion. High-intensity stimulation studies revealed that the development of convulsions was not based simply on threshold reduction, but involved complex reorganization of function. Experiments with two electrodes in separate parts of the limbic system revealed that previously established convulsions could facilitate the establishment of a second convulsive focus, but that the establishment of this second convulsive focus partially suppressed the otherwise permanent convulsive properties of the original focus.
The effect of bilateral stimulation during sequential alternation of unilateral amygdaloid stimulation
GAITO, J. The effect of bilateral stimulation during sequential
alternation of unilateral amygdaloid stimulation. Bulletin of the
Psychonomic Society, 1976. in press.