The thalamic projection to the sensory neocortex of the porpoise, Phocoena phocoena.

Retrograde tracers were injected in various parts of the neocortex of the porpoise (Phocoena phocoena). Labelled thalamic neurons were plotted in three-dimensional reconstructions. The lateral geniculate nucleus projects to the visually excitable part of the lateral gyrus. Ventral parts of the medial geniculate nucleus project to the auditory area of the suprasylvian gyrus, while dorsal medial geniculate projects to the 'secondary' auditory area of the ectosylvian gyrus and to the temporal operculum. The ventrobasal and ventropostero-inferior complex projects to cortex anterior to the suprasylvian auditory area, corresponding to somatosensory function. The main projection of the inferior pulvinar is to the suprasylvian gyrus, that of the medial pulvinar to the ectosylvian gyrus, and of the lateral pulvinar to the border of the lateral and suprasylvian gyri. The lateral and posterior complexes project to perisylvian cortex. Throughout the thalamus there is a rough topographic organisation. Lateral to medial through the thalamus represents progression from medial to lateral over the cortex from lateral gyrus to perisylvian cortex. Anterior in cortex is represented by anteroventral in thalamus, and posterior in cortex by posterodorsal in thalamus.