Escape performance following exposure to inescapable shock: Deficits in motor response maintenance

13 experiments employing 607 Swiss-Webster mice investigated shock-elicited activity in a circular field and escape performance in a shuttlebox following exposure to either escapable or inescapable shock. Upon shock inception in the circular field, Ss exhibited a 2–3 sec period of constant or increasing motor excitation followed by a decline in motor activity toward or below preshock levels. Prior exposure to inescapable shock decreased the magnitude of initial excitation and increased the rate at which locomotor excitation declined. Inescapable shock did not detectably affect escape performance if escape was possible immediately upon shock onset. If escape was briefly delayed 4–6 sec until the time at which a marked decline in the shock-elicited excitation would be expected, marked deficits of escape performance were seen. Treatments that attenuated the reduction in activity produced by inescapable shock (e.g., shock interruption during test) mitigated the escape deficits. It was demonstrated that duration and intensity of inescapable shock influence later escape behavior in a manner that is highly correlated with the motor changes induced by the treatments seen in the circular field. It is concluded that the escape interference induced by inescapable shock may be interpreted in terms of a decreased tendency for shock to sustain vigorous motor activity for protracted periods. (26 ref)