Figure 11.

Normalized peak-to-peak amplitudes of the presynaptic (A) and postsynaptic (B) components of the average field potentials for individual slices as a function of angle from the site of stimulation (n = 4). Recordings from each slice were normalized as a proportion of the size of the largest response. Zero degrees represents recordings from locations either directly medial or directly lateral to the stimulating electrode; hence, 90° represents a location that is directly caudal to the stimulation site, and −90° represents a location directly rostral to the stimulation site. In every slice, there was an obvious rostrocaudal bias in the amplitude of the fields, but there was no consistent preference for rostral direction compared with the caudal direction across slices. One slice (ZB11–112) was rotated 180°, and a second series of recordings was performed. Similar patterns of results were obtained in both conditions, showing that there is rostrocaudal bias when compared with either the medial or lateral locations of the slice. Another slice (ZB11–114) had a second series of recordings performed at a greater distance from the stimulating electrode, and the rostrocaudal bias was observed at both distances. C, Mean ± SEM peak-to-peak amplitudes of the presynaptic and postsynaptic components of the rostrocaudal-most and mediolateral-most recording locations (n = 5). The size of the field potential for both components was reliably greater (paired t test, p < 0.05) at the rostrocaudal recording locations. ML, Mediolateral; RC, rostrocaudal.