Effect of the interstimulus (CS–UCS) interval on hippocampal unit activity during classical conditioning of the nictitating membrane response of the rabbit (Oryctolagus cuniculus).

Abstract

Neuronal activity (multiple unit) was recorded from the dorsal hippocampus during classical conditioning of the nictitating membrane response in the rabbit. Groups of subjects were trained with conditioned stimulus/unconditioned stimulus (CS-UCS) interstimulus intervals of 250 msec, 150 msec, or 50 msec, and an additional group received unpaired presentations of the CS and UCS, with a tone CS and a corneal air puff UCS. Increased hippocampal unit activity and nictitating membrane conditioned responses (CRs) occurred only in the 250 msec and 150 msec groups. Both the temporal distribution of hippocampal unit activity and the averaged CR topographies were strongly and similarly influenced by the CS-UCS interval, with both neuronal and behavioral response peaks occurring near the time of UCS onset The peak of hippocampal unit activity preceded the peak of the nictitating membrane CR by 30-60 msec. When the 250 msec group was shifted to a CS-UCS interval of 500 msec, the peaks of both the hippocampal unit response and the behavioral CR topography shifted in the same direction. The shift appeared to occur sooner in the hippocampal unit response. It is suggested that the hippocampus may function to provide a "temporal map" for learned behaviors

Grid cell firing may arise from interference of theta frequency membrane potential oscillations in single neurons

“…Lesions of the entorhinal cortex also impair trace conditioning (Mering and Butenko, 1982;Ryou et al, 2001), though an early study did not see such impairments (Yeo et al, 1984). In trace conditioning, hippocampal unit responses start out responding during the trace period and become timed to occur just before the conditioned response (Hoehler and Thompson, 1980;Solomon et al, 1986). These unit responses shift to fire at a new interval before behavioural responses shift to a new interval.…”

“…Stellate cells would fire at multiple different intervals after the onset of the pyramidal cell input. These stellate neurons would form stronger excitatory inputs to the hippocampus due to Hebbian modifications of connections between firing stellate neurons and the neurons in the hippocampus showing spiking response to the unconditioned stimulus (Berger and Thompson, 1978;Hoehler and Thompson, 1980;Berger et al, 1983). Subsequent presentation of the same CS will activate persistent firing in the same pyramidal cells.…”

“…Subsequent presentation of the same CS will activate persistent firing in the same pyramidal cells. These cells would drive stellate cells to fire at varying intervals, and those with strengthened connections would drive the hippocampus units that predict in advance the timing of the conditioned response (Hoehler and Thompson, 1980;Solomon et al, 1986). These mechanisms provide a potential mechanism for coding of long temporal delays which could be complementary to the delayed timing of firing shown for some pyramidal and non-pyramidal cells in perirhinal cortex (Beggs et al, 2000;McGann et al, 2001).…”

Space, time and learning in the hippocampus: How fine spatial and temporal scales are expanded into population codes for behavioral control

“…The adaptive timing model of Grossberg and colleagues Merrill, 1992, 1996;Grossberg and Schmajuk, 1989) proposed how the dentate gyrus (DG) and hippocampal field CA3 may interact to learn adaptively timed behavioral responses (e.g., Gibbon, 1991;Roberts et al, 1989;Smith, 1968) and neurophysiological cell activations (Berger et al, 1980;Berger et al, 1986;Hoehler and Thompson, 1980) during classical and instrumental conditioning. Here we describe a model of spatial processing that describes how the same DG-CA3 circuits may also learn place fields for spatial localization.…”

Neural and endocrine effects on classical conditioning: A comparison of ACTH and hippocampectomy

“…An analysis of hippocampal multipleunit activity during classical delay conditioning of the rabbit nictitating membrane (NM) response revealed a learning-dependent increase in pyramidal cell activity. Later studies have shown a near-perfect correlation between amplitude and the time course of the neural and behavioral responses (Berger & Thompson, 1978) and that the neural response shifts earlier in training than does the behavioral response when the interstimulus interval (lSI) is altered (Hoehler & Thompson, 1980). The impact of hippocampal lesions on associative learning that involves motor responding appears to be relatively subtle.…”