Figure 3.
Locations of the multielectrode array in the auditory forebrain; this figure can be used as a map to identify the location of individual sites within auditory brain regions. Electrode sites are located at the center of the colored pixels in the 4 × 8 image matrix and are referred to throughout the text by a tuple of two numbers, (i,j), where i indicates the shank number and j, the site position on the shank. Colors represent the mean level of stereotypy, calculated over the different call stimuli that have been presented to each subject. Highly stereotypic responses are associated with the primary auditory area L2, while nonstereotypic responses are associated with secondary auditory areas NCM and CMM. For every individual, distance of the multielectrode to the interhemispheric plane is indicated, and the order of sections is organized from lateral (top left) to medial (bottom right). The location of the multielectrode in bird 3 could not be anatomically verified, and distance is based on stereotaxic coordinates. The interhemispheric and multielectrode planes are approximately, but not fully, in parallel. Distances to the midline have been estimated for the center of the array; the location of individual sites may thus deviate somewhat from this estimate in the medial–lateral direction. The white dots at pixel centers indicate that the corresponding site had DPC values >0.25 for both call stimuli in at least one switching-oddball series. Orientation of the parasagittal sections is as follows: top, dorsal; bottom, ventral; left, caudal; right, rostral. The black outline caudodorsally indicates the border of nidopallium and mesopallium, not the brain surface. The solid gray lines indicate the border of L2; the dashed gray lines indicate that the border of L2 is indistinct. Hp, Hippocampus; NCM, caudomedial nidopallium; CMM, caudomedial mesopallium; L2, subdivision of field L that includes L, L2a, and L2b (between which we do not distinguish in the current study); LaM, lamina mesopallialis (Fortune and Margoliash, 1992; Vates et al., 1996). Note that the distance between the shanks in some multielectrodes may be either 400 or 200 μm.