ON THE RELATIONSHIPS BETWEEN THE STRIATUM AND THE PEDUNCULOPONTINE TEGMENTAL NUCLEUS

In this essay we consider the role of the pedunculopontine tegmental n ucleus as a striatal output station. We review the relevant anatomical , electrophysiological, behavioral, and pathological studies and concl ude that the pedunculopontine tegmental nucleus occupies an important position in striatal outflow, receiving motor output from the dorsal s triatum and information from the ventral striatum relating to Limbic p rocesses of motivation and reinforcement. The hypothesis we present is that the pedunculopontine tegmental nucleus is at the very least an i ntegral component of the limbic-motor interface, although in discussin g this concept we also assess the likelihood that the limbic-motor int erface is in fact a distributed system-that is, that limbic-motor inte rfacing is not all done by a single structure in the central nervous s ystem but that different aspects of it are served by different systems . We present the hypothesis that the pedunculopontine tegmental nucleu s is one critical site through which limbic information concerned with motivation, reinforcement, and the construction of novel associations can gain access to a stream of motor outflow coming from the caudate- putamen and directed toward pontomedullary systems without reference b ack to the cerebral cortex. This hypothesis is important because it hi ghlights striatal outflow, which is not processed through the cortical re-entry systems, and also emphasizes the importance of pontine syste ms in cognitive processing.