title: Sodium concentration coding gives way to evaluative coding in cortex and amygdala.
abstract: Typically, stimulus batteries used to characterize sensory neural coding span physical parameter spaces (e.g., concentration: from low to high). For awake animals, however, psychological variables (e.g., pleasantness/palatability) with complicated relationships to the physical often dominate neural responses. Here we pit physical and psychological axes against one another, presenting awake rats with a stimulus set including 4 NaCl concentrations (0.01, 0.1, 0.3, and 1.0 m) plus palatable (0.3 m sucrose) and aversive (0.001 m quinine) benchmarks, while recording the activity of neurons in two sites vital for NaCl taste processing, gustatory cortex (GC) and central amygdala (CeA). Since NaCl palatability (i.e., preference) follows a non-monotonic, "inverted-U-shaped" curve while concentration increases monotonically, this stimulus battery allowed us to test whether GC and CeA responses better reflect external or internal variables. As predicted, GC single-neuron and population responses reflected both parameters in separate response epochs: sodium concentration-related information appeared with the earliest taste-specific responses, giving way to palatability-related information, in an overlapping subset of neurons, several hundred milliseconds later. CeA single-neuron and population responses, meanwhile, contained only a brief period of concentration specificity, occurring just before palatability-related information emerged (simultaneously with, or slightly later than, in GC). Thus, cortex and amygdala both prominently reflect NaCl palatability late in their responses; CeA neurons largely respond to either palatable or aversive stimuli, while GC responses tend to reflect the entire palatability spectrum in a graded fashion.
authors: Department of Biology, Brandeis University, Waltham, Massachusetts 02454, USA.
authors: Brian F
authors: BF
authors: Sadacca
authors: Jason T
authors: JT
authors: Rothwax
authors: Donald B
authors: DB
authors: Katz
mesh_terms: D000200:Action Potentials / Q000187:drug effects* / Q000502:physiology; D000679:Amygdala / Q000187:drug effects* / Q000502:physiology; D000818:Animals; D002540:Cerebral Cortex / Q000187:drug effects* / Q000502:physiology; D005260:Female; D009474:Neurons / Q000187:drug effects* / Q000502:physiology; D011803:Quinine / Q000008:administration & dosage; D051381:Rats; D020318:Rats, Long-Evans; D012965:Sodium Chloride / Q000008:administration & dosage*; D013395:Sucrose / Q000008:administration & dosage; D013649:Taste / Q000187:drug effects / Q000502:physiology; D055697:Taste Perception / Q000187:drug effects* / Q000502:physiology
chemical_list: D012965:Sodium Chloride; D013395:Sucrose; D011803:Quinine