GABA shapes selectivity for the rate and direction of frequency-modulated sweeps in the auditory cortex.
In the pallid bat auditory cortex and inferior colliculus (IC), the majority of neurons tuned in the echolocation range is selective for the direction and rate of frequency-modulated (FM) sweeps used in echolocation. Such selectivity is shaped mainly by spectrotemporal asymmetries in sideband inhibition. An early-arriving, low-frequency inhibition (LFI) shapes direction selectivity. A delayed, high-frequency inhibition (HFI) shapes rate selectivity for downward sweeps. Using iontophoretic blockade of GABAa receptors, we show that cortical FM sweep selectivity is at least partially shaped locally. GABAa receptor antagonists, bicuculline or gabazine, reduced or eliminated direction and rate selectivity in approximately 50% of neurons. Intracortical GABA shapes FM sweep selectivity by either creating the underlying sideband inhibition or by advancing the arrival time of inhibition relative to excitation. Given that FM sweep selectivity and asymmetries in sideband inhibition are already present in the IC, these data suggest a refinement or recreation of similar response properties at the cortical level.
Razak
Khaleel A
KA
Department 3166, Zoology and Physiology, University of Wyoming, 1000 E. University Ave., Laramie, WY 82071, USA.
Fuzessery
Zoltan M
ZM
D000161:Acoustic Stimulation / Q000379:methods; D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001303:Auditory Cortex / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D001306:Auditory Pathways / Q000187:drug effects / Q000502:physiology; D001309:Auditory Threshold / Q000187:drug effects / Q000502:physiology*; D001640:Bicuculline / Q000494:pharmacology; D001703:Biophysics; D002685:Chiroptera; D004305:Dose-Response Relationship, Drug; D004455:Echolocation / Q000187:drug effects / Q000502:physiology*; D004558:Electric Stimulation / Q000379:methods; D018756:GABA Antagonists / Q000494:pharmacology; D007245:Inferior Colliculi / Q000166:cytology; D007478:Iontophoresis / Q000379:methods; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000187:drug effects; D010898:Pitch Perception / Q000502:physiology; D011601:Psychophysics; D011724:Pyridazines / Q000494:pharmacology; D013017:Sound Localization / Q000187:drug effects / Q000502:physiology*; D005680:gamma-Aminobutyric Acid / Q000378:metabolism* / Q000494:pharmacology
D018756:GABA Antagonists; D011724:Pyridazines; D005680:gamma-Aminobutyric Acid; C049853:gabazine; D001640:Bicuculline