Article Figures & Data
Figures
- Figure 1.
Subjects in the experimental group were given excitotoxic lesions of the complete hippocampus. A, Representative photomicrograph of tissue from a sham-operated control (left column) and hippocampal-lesioned rat (right column). Substantial cell loss was observed throughout the dorsal and ventral hippocampus. B, The drawing depicts the largest (in gray) and smallest (in black) lesion selected from all subjects included in the study, shown here according to the atlas of Paxinos and Watson (1997).
- Figure 2.
Hippocampal-lesioned subjects were able to form a memory of the trace relationship when trained with the CTC procedure but not when trained with trace conditioning. A, This schematic represents the temporal relationship between the CS and US for a single trial for the following four conditioning procedures: trace, CTC, simultaneous, and delay conditioning. B, The percentage of change in movement from the baseline was calculated to quantify conditioned fear to the CS during testing. Rats with hippocampal lesions that were trained with delay conditioning showed conditioned responding, which indicates that the lesions did not disrupt conditioning on tasks that do not require the hippocampus. Unlike sham-operated controls, rats with hippocampal lesions trained with trace conditioning did not show conditioned responding. However, rats with hippocampal lesions trained with the CTC procedure showed significant responding at levels similar to their sham-operated counterparts. Because lesioned subjects trained with simultaneous conditioning alone did not emit conditioned responses, the responding expressed by subjects in the CTC lesion group cannot be attributed to the simultaneous component of the training procedure. Together, these results suggest that rats with lesions of the hippocampus can form a memory of the CS–US association if they are trained with CTC, in which contiguity is restored. Error bars indicate SEM.
