Fig. 12.

Optimal trace conditioning depends on adequate hippocampus function. (a) To simulate partial lesions of the hippocampus before any training trials occur in trace conditioning, scalar β _H in the hippocampal excitation term in Eq. 16 was progressively decreased. This was followed by 20 training trials, with unconditioned stimulus (US) onset at 750 ms, US duration = 50 ms, and US amplitude = 1. The results of retention testing are shown for the activities of sensory cortex (S), orbitofrontal cortex (O), hippocampus (H), amygdala (A), hippocampal adaptive timing (R), and the pontine nuclei (P). These graphs show a marker for the US presented in training for reference only (vertical dashed lines). The conditioned stimulus (CS) is also represented (vertical solid lines). Compared with normal retention testing results after 20 acquisition trials results (solid line), a 50 % decrease (dashed line) gave a small reduction in conditioned response (CR) peak amplitude and retained good timing while an 80 % decrease (dotted line) caused deficits in both amplitude and timing. (b) While extended training (60 trials rather than 20) with 80 % ablation shows minor improvement in the amplitude and timing of R, the amplitude and timing of P remain too small to support a normal CR. An intact hippocampus is thus required for efficient trace conditioning