(A) Inset i: Schematic of the lamprey brain showing the visual (blue) and electrosensory (red) afferents targeting the optic tectum (OT). Inset ii: Photomicrograph of the optic tectum in a transversal view showing the retinal afferents reaching the most superficial layers (red), and the octavolateral fibers innervating the intermediate layers (green). Inset iii: Morphology of an output neuron in the deep layer retrogradely labeled following a tracer injection in the middle rhombencephalic reticulospinal nucleus (MRRN) and filled intracellularly with Neurobiotin while performing whole-cell recordings. Output cells extend their dendrites to the intermediate and superficial layers where the electrosensory and the visual inputs enter and terminate, respectively. Abbreviations: SL, superficial layer; IntL, intermediate layer; DL, deep layer. Scale bars: Inset ii, 100 µm; Inset iii, 50 µm. (B) Experimental settings for performing extracellular recordings during multisensory integration in the optic tectum. Dorsal view of the preparation, including the brain, the eyes and electrosensory areas (depicted by the skin patches; for more information see Bodznick and Preston ), while driving output activity with light and electrical stimuli that are spatiotemporally aligned in the immediate surrounding. Abbreviations: rec: extracellular recording electrode. (C) Rectified local field potentials obtained from visual (inset i), electrosensory (inset ii) and bimodal sensory activation (inset iii). Upper traces show sensory stimulation before (black), and after local application of 10 μM gabazine (green). Horizontal dotted lines illustrate the level of peak activity during control. (D) Sensory response against stimulus duration (50–1000 μs) for visual, electroreceptive and bimodal activation, with and without local inhibition. The integral under the curve of rectified local field potentials, as those shown in C, is plotted on the y-axis and normalized to the maximum bimodal response measured during control (n = 13). Paired t-test gave statistical significance as indicated (**p<0.01, ***p<0.001).