Taste coding strategies in insular cortex

Abstract

While the cortical representation of sensory stimuli is well described for some sensory systems, a clear understanding of the cortical representation of taste stimuli remains elusive. Recent investigations have focused on both spatial and temporal organization of taste responses in the putative taste region of insular cortex. This review highlights recent literature focused on spatiotemporal coding strategies in insular cortex. These studies are examined in the context of the organization and function of the entire insular cortex, rather than a specific gustatory region of insular cortex. In regard to a taste quality-specific map, imaging studies have reported conflicting results, whereas electrophysiology studies have described a broad distribution of taste-responsive neurons found throughout insular cortex with no spatial organization. The current collection of evidence suggests that insular cortex may be organized into a hedonic or “viscerotopic” map, rather than one ordered according to taste quality. Further, it has been proposed that cortical taste responses can be separated into temporal “epochs” representing stimulus identity and palatability. This coding strategy presents a potential framework, whereby the coordinated activity of a population of neurons allows for the same neurons to respond to multiple taste stimuli or even other sensory modalities, a well-documented phenomenon in insular cortex neurons. However, these representations may not be static, as several studies have demonstrated that both spatial representation and temporal dynamics of taste coding change with experience. Collectively, these studies suggest that cortical taste representation is not organized in a spatially discrete map, but rather is plastic and spatially dispersed, using temporal information to encode multiple types of information about ingested stimuli. Impact statement The organization of taste coding in insular cortex is widely debated. While early work has focused on whether taste quality is encoded via labeled line or ensemble mechanisms, recent work has attempted to delineate the spatial organization and temporal components of taste processing in insular cortex. Recent imaging and electrophysiology studies have reported conflicting results in regard to the spatial organization of cortical taste responses, and many studies ignore potentially important temporal dynamics when investigating taste processing. This review highlights the latest research in these areas and examines them in the context of the anatomy and physiology of the insular cortex in general to provide a more comprehensive description of taste coding in insular cortex.

Glucagon-Like Peptide 1 and Taste Perception: From Molecular Mechanisms to Potential Clinical Implications

“…In both rodents and primates, thalamic afferents terminate at the primary gustatory cortex (GC) in the anterior insula of the temporal lobe, where taste coding can further be distinguished [ 85 ]. Gustatory cortex differentiates the subtleties of salty, sweet, sour, bitter, and umami.…”

“…Gustatory cortex differentiates the subtleties of salty, sweet, sour, bitter, and umami. This brain area also integrates other multisensoric modalities including thermal, mechanical, visceral, and nociceptive stimuli [ 85 , 86 , 87 ]. Individual response of GC neurons to tastants are either selective to tastens or more broadly tuned.…”

“…Optical imaging in animal studies identified four distinctive spatial patterns representing sweet, bitter, salty, and sour taste modalities, but no region was clearly specific to a single modality [ 88 , 89 ]. Similarly, functional imaging and electrophysiology studies in humans showed distinctive spatial patterns for five taste modalities as well as overlapping broad distribution of taste-responsive neurons found throughout insular cortex with no spatial organization [ 85 , 90 ]. The central responses to tastants has been topographically represented with different neuroimaging studies including calcium-imaging studies of single neurons and ultra-high resolution functional magnetic resonance imaging that enable one of the highest topographical resolution at a finer scale [ 10 , 90 ].…”

Intraperitoneal injection of lithium chloride induces lateralized activation of the insular cortex in adult mice

“…Damage involving the insula disrupts addiction to cigarette smoking in patients, demonstrating a role for the insular cortex in the representation of conscious bodily urges [ 10 ]. Researches in rodents confirm that the insular cortex is involved in chronic pain [ 11 , 12 ], feeding behavior [ 13 ], drug addiction [ 14 , 15 ], cardiac arrhythmia [ 16 ], taste coding [ 17 , 18 ] and taste aversive memory [ 19 , 20 ]. Inactivation or damage of the insular cortex prevents the urge to seek amphetamine [ 14 , 15 ], opiate [ 21 ] or alcohol [ 22 ], blunts the signs of malaise induced by acute lithium administration [ 13 , 14 ] and impaired taste aversive learning [ 23 , 24 ].…”

Intraperitoneal Injection of Lithium Chloride Induces Lateralized Activation of the Insular Cortex in Adult Mice

“…Researches in rodents con rm that the insular cortex is involved in chronic pain [11,12], feeding behavior [13], drug addiction [14,15], cardiac arrhythmia [16], taste coding [17,18] and taste aversive memory [19,20]. Inactivation or damage of the insular cortex prevents the urge to seek amphetamine [14,15], opiate [21] or alcohol [22], blunts the signs of malaise induced by acute lithium administration [13,14] and impaired taste aversive learning [23,24].…”