Modality specificity of neuronal responses within the cat's insula

Abstract

1. Electrophysiological recordings of single-unit responses, multiunit responses, and electrically evoked field potentials have been made using carbon fiber-containing micropipettes in cats anesthetized with barbiturate and immobilized with gallamine triethiodide. Recording sites sampled cortical regions throughout the insula, including zones more ventrally situated and more rostral and caudal than those described in the preceding, companion paper. One-hundred eleven cells in total were tested with a battery of different types of stimuli. 2. Stimuli were divided into two classes, according to either the intensity of the stimulus or its form. These are called physiological forms, or levels of stimulation, and nonphysiological forms or levels. The nonphysiological forms of stimuli for visual, somatosensory, and auditory modalities consisted of (for visual stimuli): 1) electrical stimulation of the optic nerve or 2) bright flashes light at 100% contrast; for somatosensory, electrical stimulation of the radial nerve by implanted cuff electrodes; and for auditory, stimulation with bursts of white noise generated at high intensities (80-100 dB) or with a loud click stimulus. Physiologically relevant levels of stimuli for these same modalities were: moving bars of light projected onto a tangent screen in front of the animal (visual); light cutaneous deformation, hair displacement, and light pressure delivered to various regions on the surface of the cat's body with hand-held probes, or delivered manually (somatosensory); and white noise generated at low intensities (ca. 40 dB) (auditory). 3. Cells situated in dorsal insular regions responded to visual stimuli when levels of sensory activation were employed using natural means, within normal, physiologically relevant limits. Responses to auditory or somatosensory stimulation were observed in this region only when very intense forms of "natural" stimulation, or when electrical stimulation (nonphysiologically relevant levels of stimulation) was delivered. In this latter case, the same cells in several instances could be made to appear polymodally responsive. With cells situated in ventral insular regions, some polymodal responses to physiologically relevant levels of stimulation were noted, although it was considerably more common to obtain unimodal responses. Nonphysiological levels of activation yielded evidence for a polymodal convergence onto the greater proportion of cells recorded. 4. Field potential recordings with microelectrodes revealed widely overlapping representations of all modalities in both dorsal and ventral regions of the insula, irrespective of the sensitivity displayed by the local neuronal r

Insular cortex and neighboring fields in the cat: A redefinition based on cortical microarchitecture and connections with the thalamus

“…Widely tuned auditory responses have been described in the anterior sylvian gyrus (Woolsey, 1960;Reale and Imig, 1980). As a whole, our findings are compatible with the notion that AS and VAE are functionally organized as a mosaic of cortical microdomains responsive either to visual or auditory stimuli (Hicks et al, 1988b).…”

The Sensory Insular Cortex Mediates the Stress-Buffering Effects of Safety Signals But Not Behavioral Control

“…The current results suggest that the Si may participate with the striatum and/or the amygdala to process safety signals. The Si in many species receives multisensory input that includes somatosensory, auditory and visual information (Loe and Benevento, 1969; Benedek et al, 1986; Cechetto and Saper, 1987; Benedek and Hicks, 1988; Hicks et al, 1988b, a; Hanamori et al, 1998; Zhang and Oppenheimer, 2000; Bamiou et al, 2003; Rodgers et al, 2008) and so it is well suited to develop the association or contingency between the signal and the absence of the stressor. Indeed when presented with stimuli from different modalities, the Si exhibits superlinear evoked potentials which suggest multisensory processing (Rodgers et al, 2008).…”

Brain responses to auditory and visual stimulus offset: Shared representations of temporal edges

“…Animal studies suggest that the insular cortex receives auditory and visual inputs via multiple pathways from primary sensory cortices, multisensory regions and, moreover, via subcortical projections from thalamic nuclei [Graybiel, 1973;Guldin and Markowitsch, 1984;Hicks et al, 1988]. Moreover, an anatomical connectivity between insula and STS has been suggested by studies using diffusion tensor imaging to map white matter fascicles in the human brain [Catani et al, 2002].…”

“…We, therefore, tentatively hypothesize that these regions are capable to combine modality-specific features arising from the same object based on the synchrony of their temporal occurrence into a complex object representation, since STS and insula are known to be crucially involved in the multisensory processing of complex audiovisual objects [Amedi et al, 2005;Beauchamp et al, 2004a,b;Raij et al, 2000]. They receive inputs from unimodal cortices as well as r Brain Responses to Auditory and Visual Stimulus Offset r r 731 r from subcortical structures [Graybiel, 1973;Guldin and Markowitsch, 1984;Hicks et al, 1988;Seltzer et al, 1996] and are thus ideally located for the integration of auditory and visual information.…”