Oligosynaptic inhibition mediated by group Ia afferents from flexor digitorum superficialis to wrist flexors in humans.

Effects of low-threshold afferents from the flexor digitorum superficialis (FDS) to the flexor carpi radialis (FCR), flexor carpi ulnaris (FCU) and extensor carpi ulnaris (ECU) motoneurons were examined using a post-stimulus time-histogram (PSTH) and electromyogram-averaging (EMG-A) methods in seven healthy human subjects. Electrical conditioning stimulation to the median nerve branch innervating FDS with the intensity immediately below the motor threshold was delivered. In the PSTH study, the stimulation produced a trough (inhibition) in 19/44 (43%) of FCR and 17/41 (41%) of FCU motor units.