ABSTRACT
Selective attention and motor commands are both considered as central efferent programs acting upon specific restricted motor and sensory neuronal pools. Descending efferent activity controls either motor neurons or inter-neurons mediating segmental and ascending sensory flow; motor commands thus influence sensory relays, and efferences directed toward sensory channels modulate motor reactivity.
If selective attention uses similar efferent mechanisms as those involved in motor commands, it becomes of interest for the study of attention to examine the influence of limited active movements upon the sensory information carried over the pathways involving the actively moved limb. The first part of this chapter reports results from experiments on cats showing that during movement somatic volleys are reduced at the first lemniscal relay and possibly reamplified at the specific thalamic relay.
The second part reports experiments in man linking attention to orienting reaction, and hence to efferent programs. During passive attention, unexpected stimuli induce late cortical waves (N2 and P3), considered as components of the generalized orienting response and possibly reflecting the release of stimulus identification programs. Attention to expected stimuli has the same effects as the repetition of an unexpected stimulus: the generalized orienting reaction habituates and focuses on structures involved in the processing of attended stimuli. Further habituation of this localized orientation reaction is prevented during active attention.
The third part presents data from an experiment on man using cutaneous reflexes of the lower limbs. The results show that the nociceptive reflexes are indeed specifically enhanced in the leg to which the subjects pay attention as compared to the reflexes in the leg that is nonattended.
