Excitability of EEG "synchronizing" and "desynchronizing" neurones in the thalamus and the brain-stem of the cat. I. The applicability of strength-duration determinations and conditioning-test technique

1. 1. In the encéphale isolé cat the excitability was determined of thalamic neurones from which the cortical recruiting response could be elicited by low frequency electrical stimulation. 2. 2. Strength-duration curves were drawn which behaved according to the equation: I_t{plus 45 degree rule}I_τ=1{plus 45 degree rule}(1-e^-t{plus 45 degree rule}τ) 3. 3. The time constant (τ) of the thalamic cells involved was measured by the conditioning-test shock technique and was found, within the limits of experimental error, to be the same as the time constant of the strength-duration curve. 4. 4. It is shown that this technique permits an estimate of the absolute and the relative refractory periods of the stimulated cells. 5. 5. An explanation of these findings is proposed.