Multisensory integration in the basal ganglia.

Sensorimotor co-ordination in mammals is achieved predominantly via the activity of the basal ganglia. To investigate the underlying multisensory information processing, we recorded the neuronal responses in the caudate nucleus (CN) and substantia nigra (SN) of anaesthetized cats to visual, auditory or somatosensory stimulation alone and also to their combinations, i.e. multisensory stimuli. The main goal of the study was to ascertain whether multisensory information provides more information to the neurons than do the individual sensory components. A majority of the investigated SN and CN multisensory units exhibited significant cross-modal interactions. The multisensory response enhancements were either additive or superadditive; multisensory response depressions were also detected. CN and SN cells with facilitatory and inhibitory interactions were found in each multisensory combination. The strengths of the multisensory interactions did not differ in the two structures. A significant inverse correlation was found between the strengths of the best unimodal responses and the magnitudes of the multisensory response enhancements, i.e. the neurons with the weakest net unimodal responses exhibited the strongest enhancement effects. The onset latencies of the responses of the integrative CN and SN neurons to the multisensory stimuli were significantly shorter than those to the unimodal stimuli. These results provide evidence that the multisensory CN and SN neurons, similarly to those in the superior colliculus and related structures, have the ability to integrate multisensory information. Multisensory integration may help in the effective processing of sensory events and the changes in the environment during motor actions controlled by the basal ganglia.