Are Bimodal Neurons the Same throughout the Brain?

Excerpt

Although it has been generally assumed that bimodal neurons are essentially the same, an insightful study of multisensory integration in bimodal SC neurons demonstrated that bimodal neurons exhibit different functional ranges (Perrault et al. 2005). Some bimodal neurons were highly integrative and exhibited integrated, superadditive (combined response > sum of unisensory responses) responses to a variety of stimulus combinations, whereas others never produced superadditive levels despite the full range of stimuli presented. In this highly integrative structure, approximately 28% of the bimodal neurons showed multisensory integration in the superadditive range. Thus, within the SC, there was a distribution of bimodal neurons with different functional ranges. Hypothetically, if this distribution were altered, for example, in favor of low-integrating bimodal neurons, then it would be expected that the overall SC would exhibit lower levels of multisensory processing. Because many studies of cortical multisensory processing reveal few examples of superadditive levels of integration (e.g., Meredith et al. 2006; Clemo et al. 2007; Allman and Meredith 2007; Meredith and Allman 2009), it seems possible that bimodal cortical neurons also exhibit functional ranges like those observed in the SC, but do so in different proportions. Therefore, the present investigation reviewed single-unit recording data derived from several different cortical areas and the SC (as depicted in Figure 4.1) to address the possibility that bimodal neurons in different parts of the brain might exhibit different integrative properties that occur in area-specific proportions.