The 3-channel Lissajous' trajectory of the auditory brain-stem response. VI. Effects of lesions in the cat

Two discrete studies of lesions (sectioning the auditory nerve and mid-sagittal brain-stem) were performed in 5 adult cats to determine the relationship between planar-segment formation and underlying generator activity. The experiments gave 2 major results: (1) Section of the VIII nerve at the brain-stem resulted in loss of potentials after wave II and almost total loss of wave II in most traces. In the time interval of planar segments a1, a2 and b1, only a single planar loop remained after sectioning the VIII nerve, and its orientation corresponded to that of the pre-surgical planar segment a1. (2) Whereas mid-sagittal sectioning of the brain-stem considerably reduced waves 4, 5 and 7 in vector amplitude plots, planar analysis showed that planar segments c2, c3, c4 and d1 were reduced to the simpler configuration of a line in voltage-space, and that planar segments d2, d3 and d4 were reduced in size and shifted in orientation. These results suggest the following hypotheses: (1) planar segment a1 must represent activity arising from the VIII nerve peripheral to its entry point into the brain; (2) VIII nerve activity can extend into the time that the cochlear nuclear complex is active; (3) an additional generator, probably the cochlear nuclear complex, contributes to the negativity observed after wave I; (4) planar segments c2, c3, c4 and d1 represent activity from generators whose input is from the contralateral ear. Some of the contributors to planar segments d2, d3 and d4 are activated by pathways ipsilateral to the stimulated ear, while the remaining portion is contralaterally activated.