MONOSYNAPTIC AND POLYSYNAPTIC REFLEXES IN MAN DURING ATTENTION

Extension and flexion monosynaptic reflexes and flexion polysynaptic reflexes were studied during activation produced by two tests requiring the sustained attention of the subject. The psychological tests used were sufficiently difficult to produce, in all the subjects, significant variations in the respiration and heart rates and in the amplitude of the evoked potentials in the cortex. 1. 1. The soleus tendon reflex was increased considerably. 2. 2. A comparison of the monosynaptic responses of the soleus produced either by cutaneous stimulation of the group Ia afferent fibres (H reflex) or by percussion of Achilles' tendon (tendon reflex), did not reveal large differences in the responses. The effect contrasted with the modifications observed in the course of the Jendrassik manoeuvre (clenching the fist) which modified little the H reflex but increased considerably the ankle jerk and seemed to act preferentially on the fusimotor system. 3. 3. The tendon reflex of the biceps femoris (flexor) was increased in all cases. 4. 4. The polysynaptic reflex (of flexion) of the biceps produced by cutaneous stimulation of the sural group II afferents was significantly increased in all cases. 5. 5. On the contrary, the polysynaptic reflex of the biceps, produced by stimulation of the group III afferents of this nerve, was inhibited. 6. 6. According to the type of test used and the reflexes studied, variations were observed within the same subject and between subjects in the strength of the responses. Nevertheless, the results obtained were extremely significant statistically. 7. 7. The simultaneous recording of the different reflexes studied confirmed the stereotyped motor effects of attention. The stereotyping is identical to the observed in animals when the supra-bulbar reticular formation is stimulated . © 1969.