ABSTRACT

It is a basic tenet of neuroscience that different neural circuits underlie different functions or behaviors. For the œeld of multisensory processing, however, this concept appears to be superseded by the system’s requirements: convergence of inputs from different sensory modalities onto individual neurons is the requisite, deœning step. This requirement is fulœlled by the bimodal neuron, which has been studied for half a century now (Horn and Hill 1966) and has come to represent the basic unit of multisensory processing (but see Allman et al. 2009). Bimodal neurons are ubiquitous: they are found throughout the neuraxis and in nervous systems across the animal kingdom (for review, see Stein and Meredith 1993). Bimodal (and trimodal) neurons exhibit suprathreshold responses to stimuli from more than one sensory modality, and often integrate (a signiœcant response change when compared with unisensory responses) those responses when the stimuli are combined. As revealed almost exclusively by studies of the superior colliculus (SC), bimodal neurons integrate multisensory information according to the spatial, temporal, and physical parameters of the stimuli involved (for review, see Stein and Meredith 1993). The generality of these principles and the

4.1 Introduction ............................................................................................................................ 51 4.2 Methods .................................................................................................................................. 52

4.2.1 Surgical Procedures .................................................................................................... 52 4.2.2 Recording .................................................................................................................... 52 4.2.3 Data Analysis .............................................................................................................. 53

4.3 Results .....................................................................................................................................54 4.3.1 Anterior Ectosylvian Sulcal Cortex ............................................................................54 4.3.2 Posterolateral Lateral Suprasylvian Cortex ................................................................54 4.3.3 Rostral Suprasylvian Sulcal Cortex ............................................................................ 59 4.3.4 Superior Colliculus ..................................................................................................... 59

4.4 Discussion ...............................................................................................................................60 4.4.1 Bimodal Neurons with Different Integrative Properties ............................................60 4.4.2 Bimodal Neurons in SC and Cortex Differ ................................................................60 4.4.3 Bimodal Neurons in Different Cortical Areas Differ .................................................60 4.4.4 Population Contribution to Areal Multisensory Function .......................................... 61 4.4.5 Methodological Considerations .................................................................................. 62

4.5 Conclusions ............................................................................................................................. 63 Acknowledgments ............................................................................................................................ 63 References ........................................................................................................................................ 63

broadness of their applicability appeared to be conœrmed by similar œndings in cortical bimodal neurons (Wallace et al. 1992) and overt multisensory behaviors (Stein et al. 1989).