THE ROLE OF THE PEDUNCULOPONTINE TEGMENTAL NUCLEUS IN RELATION TO CONDITIONED MOTOR-PERFORMANCE IN THE CAT-II - EFFECTS OF REVERSIBLE INACTIVATION BY INTRACEREBRAL MICROINJECTIONS

The effects of reversible pharmacological manipulation of the neuronal activity in the pedunculopontine tegmental nucleus (PPTg) on the perf ormance of a conditioned movement was studied in two freely moving cat s. The microinjections were given in regions where, in the same subjec ts, we had previously identified neurons with context-dependent early activity after a trigger stimulus and with reinforcement-related activ ity. The subjects were conditioned to perform a forelimb-flexion movem ent controlled by a simple reaction-time task. In addition, one subjec t was trained to execute the same flexion movement, but delayed after the trigger stimulus. Food pellets were used as the reinforcer. Lidoca ine injections (1 mu l of 2% solution, injected over a 6-min period) i nduced a transient arrest of performance within minutes. The cessation of performance could be preceded by behavioral signs such as meowing, attempt to escape from the experimental booth, licking, or stereotype d posture. No rotational behavior could be observed. The effects of li docaine could be mimicked in one subject by an extinction procedure. M uscimol injections (two injections of 0.2 mu g in 1 mu l, tested in on e subject) also induced arrest of performance, but the return to pre-i njection level of performance could not be obtained within the time of the test session. The quantitative analysis of reaction times and of inter-trial intervals showed that altering PPTg activity affected inte r-trial intervals, but only slightly affected the reaction times. It i s speculated that the PPTg is involved in the reinforcement process re lated to selecting the appropriate motor program.