Mesial prefrontal cortical lesions and timidity in rats. I. Reactivity to aversive stimuli.

Two experiments were conducted to assess the degree to which mesial prefrontal cortical (MFC) lesions in male rats alter the behavioral manifestations of fear (timidity). The first experiment gauged the reactivity to the threat of electroshock. MFC lesions did not alter the incidence of freezing in a box associated with shock. MFC and sham-lesioned subjects made few errors when they were required to run from an open field into a small compartment to avoid shock, but displayed the classical MFC deficit when forced to run in the opposite direction. MFC lesions also increased the latency to enter an open field when the field was novel or aversive, but not when it was familiar. In a second experiment, it was found that the classical MFC hoarding deficit occurred when rats had to traverse an illuminated but not a dark runway to reach food pellets. Similarly, burrowing was normal when subjects had to burrow to escape from an open field, but not when they had to enter an open field to burrow. It is concluded that damage restricted to MFC enhances timidity, and that this effect accounts for several behavioral alterations that contribute to the MFC lesion syndrome.