Changes of somatosensory evoked potentials in man as correlates of transcortical reflex mediation?

Somatosensory evoked potentials (SSEP) from the scalp of the sensori-motor cortex were recorded together with long latency reflexes in the EMG of the contralateral biceps muscle in 17 human subjects, who were instructed to compensate a sudden biceps stretch. In this 'compensate' condition the earliest deviation from the shape of the SSEP obtained in a 'let go' situation (exhibiting only short latency reflexes) occurred as early as 35-40 ms. The results indicate that SSEP changes associated with the occurrence of long latency reflexes might be compatible with a transcortically mediated reflex activity.