Anticipatory cerebellar responses during somatosensory omission in man

The traditional view of cerebellum is a structure that modifies and synchro nizes elements of motor performance. Recent evidence indicates that human c erebellum is involved in a wide range of nonmotor sensory and cognitive fun ctions. A common feature in these diverse motor and nonmotor tasks may be t he capacity of cerebellar neuronal circuits to process and anticipate senso ry input with high temporal acuity. We present evidence supporting this hyp othesis from measurements of the magnetic field at the scalp evoked by neur onal population activity in human cerebellum. Intermittent electrical stimu lation of the finger and the median nerve elicited stimulus-locked cerebell ar responses with oscillatory components at 6-12 Hz and 25-35 Hz. Sustained oscillatory activity followed random stimulus omissions, with initiation o f cerebellar responses Frier to the next overt stimulus. These responses in dexed processing of temporal features of somatosensory input independent of motor performance or response. The refractory behavior of the responses su ggested that a neuronal trace of the temporal pattern of somatosensory stim ulation remained in cerebellar circuits for 2-4 s. The cerebellar activity elicited by violation of an established temporal pattern was enhanced when attention was directed to somatosensory stimuli, in concordance with recent imaging studies suggesting participation of cerebellum in attentional netw orks. The attentional enhancement of the cerebellar responses supports the salience of cerebellar activity in the processing of purely somatosensory i nput. The short-term maintenance of cerebellar templates for predictable se nsory input may reflect a physiological substrate for fine-grained temporal tuning and optimization of performance in large-scale sensory and integrat ive systems. (C) 2000 Wiley-Liss, Inc.