Footshock-produced excitation and inhibition of activity in rats

Hooded rats received five 1-sec shock presentations of 0.3, 0.5, or 1.0 mA. Activity measures recorded during each 30-sec intershock interval and at various retention intervals (.10, 2.5, and 24 h) following footshock (FS) indicated that (a) 5 sec after FS activity is directly related to shock intensity, while 10–30 sec following FS activity is inversely related to shock intensity; (b) the rate of decline in activity following FS increases with successive shock presentations; (c) activity is greater 10 h after FS than at a 2.5- or 24-h retention interval; and finally (d) shock compartment confinement increased activity and resulted in a substantial alteration in the form of retention curve in the 0.3-mA group but had lesser effects upon the retention curves of the 0.5- and 1.0-mA groups. The data were interpreted as supporting the hypothesis that the “incubation effect” is a result of a decline of the activating effects of FS.