Blurry Topography in the Cortical Target-Distance Maps of Bats
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1
Havana University, Dept. of Animal and Human Biology, Cuba
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2
Goethe-Universität, Institut für Zellbiologie und Neurowissenschaft, Cuba
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3
University of Potsdam, Institute of Biochemistry and Biology, Germany
Echolocating bats use the time elapsed from biosonar pulse emission to the arrival of echo to infer target-range. Such time (known as pulse-echo delay) is encoded in the auditory cortex by delay-tuned neurons that respond to specific echo-delays. In the auditory cortex of Pteronotus parnellii, Pteronotus quadridens, Carollia perspicillata and Rhinolophus rouxi the delay-tuned neurons are clustered forming specialized computational maps that control the perception of target-distance. Target-distance maps were described using the neuronal best delay and characteristic delay as a measure of neuronal delay-tuning. The best delay and characteristic delays are calculated as the delays evoking maximum responses at a fixed echo-level. However, it is well-known that the delay-tuned neurons respond to several combinations of pulse-echo delays and echo-levels and therefore their response is better described by delay response fields (DRF). DRFs are constructed from the neuronal response to combinations of delays and echo-levels that bats are likely to encounter in natural situations. We explored the topographical arrangement of neurons in the FM/FM area of P. quadridens, according to metrics used for characterization of delay response fields. Such metrics were measured in the neuronal threshold curves; and they included the characteristic delay (delay at the tip of the threshold curve), best delay (delay that evoked the maximum response in the entire response field), and minimum and maximum response delays. Bats rely on precise target-distance computations for an accurate flying performance. Therefore we expected cortical computational maps to have a similar organization whether characteristic delay, best delay, minimum or maximum response delays were analyzed. The results contradicted our initial hypothesis. We found that cortical units display a clear rostro-caudal organization if the characteristic delay and maximum response delays are analyzed. However, such organizational pattern is less clear if the best delay and minimum response delay are analyzed. The minimum response delay and the best delay maps, contain disproportionately large regions dedicated to the processing of short-delays. The latter indicates a loss of fine grain resolution in cortical maps when the incoming information of decreasing echo delay is processed during the final phase of prey capture. Therefore cortical target-range computational maps of bats are more ambiguous than previously thought. We also examined the response latency of delay-tuned neurons and found that in response to short-echo delays (i.e. <8 ms) units respond with a wide range of latencies (i.e. between 18-32 ms). Bats species that lack cortical target-distance computational maps also respond to short echo-delays with wide range of latencies and this feature has been suggested as one cue feature for the assembling of temporally distant events into an overall acoustic scene. We suggest that bat species with and without cortical computational target-distance maps might use a similar latency-based mechanism to build-up acoustic scenes. Such mechanism does not necessarily require topographically organized maps but it could profit from the “housekeeping” advantages it provides.
Keywords:
Auditory Cortex,
bats,
cortical topography,
pulse-echo delay,
target range
Conference:
Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012.
Presentation Type:
Poster Presentation (see alternatives below as well)
Topic:
Sensory: Audition
Citation:
Macias
S,
Hechavarría
JC,
Vater
M,
Mora
EC and
Koessl
M
(2012). Blurry Topography in the Cortical Target-Distance Maps of Bats.
Conference Abstract:
Tenth International Congress of Neuroethology.
doi: 10.3389/conf.fnbeh.2012.27.00120
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Received:
25 Apr 2012;
Published Online:
07 Jul 2012.
*
Correspondence:
Dr. Silvio Macias, Havana University, Dept. of Animal and Human Biology, Havana, 10400, Cuba, silvio.macias727@gmail.com