Peripheral input to L4 neurons whose activity is modulated by neck rotation.

We studied, in decerebrate cats, peripheral input from the ipsilateral hindlimb to L4 neurons whose activity was modulated by neck rotation ('neck-modulated neurons'). Most neurons received convergent input from muscle, cutaneous and mixed nerves. In about half the neurons muscle input consisted of short-latency group I or group II excitation or inhibition, with group II effects far more frequent. Such synaptic actions were produced almost entirely by stimulation of quadriceps or sartorius. In the other neurons muscle afferents produced only late, diffuse excitation or inhibition, with thresholds usually in the group III range.