Fig. 3. Schematic diagram of delay (A), contextual (B), and trace (C) fear conditioning. In delay conditioning (A), the conditioned stimulus (CS), e.g., a tone precedes and overlaps with the unconditioned stimulus (US), e.g., foot shock. In contextual conditioning (B), the US is administered in a conditioning context. In trace fear conditioning (C), the CS and US are separated by a stimulus-free “trace interval” (dashed line).
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