Changes in central somatosensory pathways accompanying reaction movements

Preparatory delay activity in the monkey parietal reach region predicts reach reaction times

To acquire something that we see, visual spatial information must ultimately result in the activation of the appropriate set of muscles. This sensory to motor transformation requires an interaction between information coding target location and information coding which effector will be moved. Activity in the monkey parietal reach region (PRR) reflects both spatial information and the effector (arm or eye) that will be used in an upcoming reach or saccade task. To further elucidate the functional role of PRR in visually guided movement tasks and to obtain evidence that PRR signals are used to drive arm movements, we tested the hypothesis that increased neuronal activity during a preparatory delay period would lead to faster reach reaction times but would not be correlated with saccade reaction times. This proved to be the case only when the type of movement and not the spatial goal of that movement was known in advance. The correlation was strongest in cells that showed significantly more activity on arm reach compared with saccade trials. No significant correlations were found during delay periods in which spatial information was provided in advance. These data support the idea that PRR constitutes a bottleneck in the processing of spatial information for an upcoming arm reach. The lack of a correlation with saccadic reaction time also supports the idea that PRR processing is effector specific, that is, it is involved in specifying targets for arm movements but not targets for eye movements.

Gating of tactile input from the hand. II. Effects of remote movements and anaesthesia

Tactile sensations of flutter or pressure were evoked in alert human subjects by intraneural microstimulation in the median nerve. Ratings were obtained of the magnitude of sensations at threshold for conscious detection during movement of the finger to which they were projected, of neighbouring fingers or of the opposite hand. Results showed that inhibition of flutter sensation was maximal in the moved finger (48%), with a weaker graded effect from adjacent (23%) to distant (19%) fingers of the same hand. Sensations of pressure were more markedly suppressed but the gradients were similar. Movement of the opposite hand and isometric contraction of the forearm muscles had little effect. Local anaesthetic blocks of the median and other upper limb nerves counteracted most of the inhibitory effect of movement on cutaneous flutter sensation. We conclude that sensory gating is largely restricted to the moved digits, that it applies to submodalities of both flutter and pressure and that sensory gating is mostly mediated by cutaneous receptor input from the hand.