Intensity generalization with positively reinforcing intracranial stimulation

Role of the basal ganglia in the reproduction of instrumental reactions developed in response to electrostimulation of the hippocampus

A defensive instrumental conditioned reflex (CR) successively to light flashes and to electrostimulation of the dorsal hippocampus (DH) and the caudate nucleus (CN) was developed in dogs with electrodes implanted in the brain. The contralateral of the DH, CN, the accumbent nucleus (AN) and the globus pallidus (GP) were tested for reproducibility of the instrumental movement. In a second series, the percent of evoked movements was compared with the EP arising in response to signal and test stimulation. The degree of participation of the tested structures in the motivational, signal, and executive components of the CR was elucidated. In the first series the movements were practically not reproduced. In the second series, in the presence of connections from the signal to the tested structures, they were elicited only by stimulation of the AN (15%). In the same series, given bilateral connections, movements in response to the stimulation of the basal ganglia occurred somewhat more frequently (up to 28%). The stimulation of the contralateral DH elicited movements in 75-100% of cases. When stimulation of the CN became a signal, the stimulation of the AN and the GP was accompanied in 40-100% of cases by movement. Thus, the AN participates to a minimal degree in the executive component of the CR. Participation of the basal ganglia in the signal component of the CR was greatest in the third series, which indicates that intrasystemic generalization is more effective than intersystemic.

Discrimination between aversive brain stimulations: effect of stimulation parameters

Rats placed in a T maze were shown to be able to discriminate between two stimulations applied to one and the same brain site and inducing aversive effects of different magnitude. Discrimination occurred irrespective of whether the two stimulations differed in either intensity or frequency, and irrespective of whether they were applied to a medial hypothalamic or to a mesencephalic central gray site. Generalization experiments were performed in which either the stimulation parameter used to establish the discrimination or another parameter was varied. The results show that the animal's choice cannot be predicted on the sole basis of either the electrical charge/second applied or the escape latency induced.

Parametric effects in the discrimination of intracranial stimulation: some methodological and analytical issues

Rats were implanted with electrodes in the medial forebrain bundle at the level of the lateral hypothalamus. Electrical stimulation was established as a conditioned stimulus for responding in a modified two-way active shock avoidance procedure. Stimulus generalization experiments were conducted to determine the effects of pulse frequency, current intensity, pulse duration, and of train duration. It was found that the discriminative stimulus properties of the electrical stimulation co-varied in an orderly manner with variations in each of the parameters. The generalization data sets of frequency, intensity, and train duration could be fitted by linear functions in log-linear coordinates; the effects of pulse duration generated a biphasic gradient. An analysis in terms of charge revealed that train duration had the lowest slope, whereas frequency and intensity generated equally steep functions. The most striking differences occurred among conditions which were similar in terms of current intensity, pulse duration and number of pulses, but which differed in the temporal patterning of pulses. Some methodological and analytical aspects of discrimination and generalization with intracranial stimulation are discussed.