Binns KE; Salt TE; (1996) The importance of NMDA receptors for multi-modal integration in the deep layers of the cat superior colliculus. Journal of Neurophysiology, 75:920-930.

1. Many sensory events contain multi-modal information yet most sensory nuclei are devoted to the analysis of single modality information. In the deep superior colliculus (DSC) visual, auditory and somatosensory information converges on individual multi-modal neurones. The responses of multi-modal neurones are determined by the temporal and spatial correspondence properties of the converging inputs such that stimuli arising from the same event elicit a facilitated multi-modal response.

2. NMDA receptors may underlie the detection of spatial and temporal coincidence and could be involved in the generation of multi-modal facilitatory responses due to the non-linear properties of NMDA-receptor-mediated events. In order to assess the role of NMDA receptors in multi-modal integration, extracellular recordings were made from single multi-sensory neurones in the DSC of the cat.

3. The responses to visual, auditory and somatosensory stimuli alone and to multi-modal combinations of stimuli were challenged with iontophoretically applied AP5, an NMDA receptor antagonist. All responses to visual stimuli presented alone (n=9) were greatly reduced. Somatosensory responses (n=25) were usually decreased. In contrast, the responses to auditory stimulation were decreased (n=9), unaffected (n=3) or enhanced (n=5).

4. Responses to multi-modal stimulus presentations were consistently reduced during iontophoretic application of AP5, irrespective of the modalities which comprised the stimulus. The reductions of multi-modal responses were significantly greater than the sum of the reductions of responses to single-modality stimuli.

5.The data suggest, that for uni-modal stimuli, the importance of NMDA receptors in synaptic transmission of sensory responses in DSC may be dependent on the stimulus modality. Furthermore, NMDA receptors are of major importance in the integration of input from different modalities for the generation of multi-modal responses.