Photomicrographs of parvalbumin (PV) immunostaining in the white matter of the lar gibbon, showing the distribution of occasional WMICs immunoreactive to PV. (a) White matter (WM) deep to the cortex of the superior frontal gyrus, with an arrow indicating a single PV-immunoreactive WMIC. (b) PV-immunoreactive WMICs were not observed in the white matter deep to the fundus of the inferior frontal sulcus. (c and d) WM deep to the primary motor cortex, with arrows showing two PV-immunoreactive WMICs. (e) PV-immunoreactive WMICs were not observed in the white matter deep to the somatosensory cortex. (f) PV-immunoreactive WMICs were not observed in the deep white matter surrounding the claustrum (Cl). GM – grey matter, P – putamen nucleus. Scale bar in d = 250 μm and applies to d only. Scale bar in f = 500 μm and applies to a, b, c, e and f. In all images dorsal is to the top of the image and medial to the left.