Behavioral and EEG patterns in the cat coincident with systemic and intracranial stimulation with d-amphetamine sulfate during a visual discrimination task

The behavioral and electroencephalographic (EEG) effects of d-amphetamine sulfate injection into the basolateral amygdala, posterior hypothalamus, ventral hippocampus, and medial thalamic area were compared with a saline control Injection, and a central administration of amphetamine delivered via the interperitoneal cavity during a behavioral task. The order of drug administration to the respective areas in each of six adult male cats was balanced In a latin-square design. The experimental task consisted of a 50 trial complex go-no-go visual discrimination task. Each trial consisted of a 10 second reinforcement period (SD) cued by a 4 c/sec. flashing light. Bar pressing responses made during the SD period were reinforced with milk. The intertrial period was a 30 second variable interval schedule during which no reinforcement could be obtained. Quantitative measures obtained on all subject consisted of total responses, reinforced responses (SDR)» and intertrial interval responses (ITIR), Daily performances were evaluated on the basis of a ratio of intertrial interval to reinforced responses (ITIR / SDR), In addition EEG measures were obtained from electrodes Implanted in various brain loci and permanently stored on tape, EEG records were obtained on the stimulation day, while operant levels were recorded 2U and 48 hours following stimulation as well. Comparisons were made between baseline, saline, and experimental conditions for the operant behavioral results as follows: (1) Amphetamine stimulation In the basolateral amygdaloid nuclei was characterized by significant facilitation of performance at 24 and 48 hours following stimulation. (2) Posterior hypothalamic stimulation resulted in significant increases in performance at 24 and 48 hours, although not of the same magnitude as the amygdala results. (3) Hippocampal and thalamic stimulations with amphetamine were found to be non-significant in their effects on operant responses. (4) Central stimulation with amphetamine produced operant levels which trended toward facilitation at 24 hours and reached significance at 48 hours. (5) Saline administrations were found to be non-effective in influencing operant responding, differences between the saline control and baseline being non-significant. Analyses of five frequency bands in the EEG arousal spectrum were performed, concentrating solely on the amygdaloid stimulation days, with examination of brain loci confined to the lateral geniculate and visual cortex, the primary projection pathways for the visual stimulus. The principle results were as follows: (1) Amphetamine stimulation in the amygdala produced shifts in the frequency bands resulting in a dominance of power gains coincident with the photic stimulus pulsations in the band characterized by a center frequency of 40 c/sec. The result was seen in both the visual cortex and lateral geniculate. (2) Crosspower functions which measured the coherence of power in a frequency band for the two areas was calculated with the result that again the 40 c/sec. band was prevalent. The results of these findings were related to the psychopharmacological properties of amphetamine and its actions on norepinephrine, as well as neuroanatomical structures in the brain possessing high concentrations of norepinephrine. The amygdala and hypothalamus were implicated as unusually active in this context. Further implications were drawn regarding the prevalence of 40 c/sec. electrical activity as an electrophysiological correlate of learning.