Identification of a fast lemnisco‐cortical system in the cat

Of the four major components of the complex cortical response produced by stimulation of the ventral surface of the brain stem at the level of the medullary pyramids, only the first depends upon antidromic activity in pyramidal-tract fibres (Jabbur & Towe, 1961). Jabbur & Towe have also ascribed a diminutive positive deflexion, not one of the four major components, to antidromic invasion of pyramidal-tract neurones. The last and most prominent component of the complex response results from orthodromic activation of cortical neurones via the medial lemniscus system; the second and third waves of the complex response arise from activation of fibres intermingled with the medial lemniscus fibres. Because the second wave is similar in configuration to the first, is able to follow faithfully rather high stimulus rates and is resistant to asphyxia, Jabbur & Towe argued that the second component probably resulted from antidromic activity in a hitherto undefined descending tract or in an 'aberrant' pyramidal bundle. On the contrary, as this paper will show, the second component results from orthodromic activation of cortical neurones via a system of fibres possessing at least one subcortical synapse. The third component will also be attributed to orthodromic activity.