The pedunculopontine tegmental nucleus: a role in cognitive processes?

The cholinergic pedunculopontine tegmental nucleus, located in the brainstem and part of the reticular formation, has been traditionally linked to motor function, arousal and sleep. Its anatomical connections, however, raise the possibility that the pedunculopontine tegmental nucleus is also involved in other aspects of behaviour such as motivation, attention and mnemonic processes. This is of obvious importance, since the pedunculopontine tegmental nucleus undergoes degeneration in human neurodegenerative disorders also characterized by attentional and/ or mnemonic deficits. Moreover, recent behavioural animal work suggests that cognitive processes may be represented in the pedunculopontine tegmental nucleus. The difficulty that faces research in this area, however, is the possible influence of cognition by other processes, such as arousal state, motivation and motor function. Nevertheless, by reviewing the literature, the pedunculopontine tegmental nucleus seems to be involved in attentional and possibly also in learning processes. These processes could be mediated by influencing cortical fuction via the thalamus, basal forebrain and basal ganglia. The involvement of the pedunculopontine tegmental nucleus in mechanisms of memory, however, seems to be rather unlikely.