Experimental design and procedure. (a) Schematic representation of the lateral view of a tree shrew brain showing the position of the stimulation electrode in the basal forebrain (BF) and the three tetrodes used for recording from primary visual cortex (V1). (b) Sample time course showing the effect of BF stimulation on spontaneous V1 LFP. Large amplitude, slow fluctuations change to a higher frequency oscillation. (c) Experimental Paradigm: The upper panel represents the “BF stim only” protocol used for measuring the effects of BF stimulation on the spontaneous LFP spectrum. The middle and lower panel represent the “BF stim grating” protocols where drifting sinusoidal gratings of different contrasts and orientations were presented, without (middle) and with interleaved BF stimulation (lower panel). The time point of BF stimulation is represented by a black arrow. (d) A cytochrome oxidase stained coronal section showing the electrode track and electrolytic lesions at 3 different depths (8200, 7200 and 1000 μm). The lowest lesion, in the region of NBM, was at the final position of the stimulation electrode.