Julio César Hechavarria Cueria
Echolocating bats crucially depend on a precise cortical computation of echo-delay to be able to localize their prey. There are two strategies known how this task could be solved. Heteroharmonic bats compute the time interval between the emission of a lower frequency harmonic in the call and the incoming echoes from a higher frequency harmonic. This type of echo-delay tuning is found in CF-FM bats, whose echolocation signal consists of a constant frequency (CF) component followed by a frequency-modulated (FM) component. (ii) In contrast, bats emitting purely frequency modulated calls (FM bats) so far are described as computing the echo delays by using call-echo pairs of similar frequencies (homoharmonic).
(1) The first aim of my project is to compare the echo-delay selectivity in neurons from the auditory cortex of the homoharmonic FM-bat species (Carollia perspicillata) with the heteroharmonic FM-bat species Pteronotus quadridens. In addition, to assess the temporal dynamics of delay-tuning computation in neuronal populations, multi-electrode recordings along the cortical echo-delay axis of the used homo- and heteroharmonic bats will be obtained.
(2) The second aim of my research project focuses on the mechanisms for the construction of echo delay-selectivity in auditory neurons from homoharmonic and heteroharmonic bats. It has been shown for the mustached bat that the basic properties of neuronal echo-delay tuning are already established on the level of the auditory midbrain. However, it is not known whether the delay tuning observed in the auditory cortex is recreated on this level, or simply relayed from lower auditory stations. To address this question I will intracellularly record cortical neurons to assess changes in membrane potential associated with delay-tuning. In addition, to test the prevalence of intracortical delay-tuning mechanisms, inhibitory and facilitatory transmitter agonists will be applied microiontophoretically.
Neurons in the inferior colliculus of the mustached bat are tuned both to echo-delay and sound duration. Macías S, Hechavarría JC, Kössl M, Mora EC.
Evolution of neuronal mechanisms for echolocation: specializations for target-range computation in bats of the genus Pteronotus. Hechavarría J.C., Macías S, Vater M, Mora EC, Kössl M.
Properties of echo delay-tuning receptive fields in the inferior colliculus of the mustached bat. Macías S, Mora EC, Hechavarría J.C., Kössl M.
Hechavarría, J.C.;Cobo, A.T.; Fernández, Y.; Macías, S.; Kössl, M.; Mora EC. 2011.Sound-evoked oscillation and paradoxical latency shift in the inferior colliculus neurons of the big fruit-eating bat, Artibeus jamaicensis.J Comp Physiol A. doi:10.1007/s00359-011-0678-x
Macías S, Mora EC, Hechavarría JC, Kössl M. 2011.Duration tuning in the inferior colliculus of the mustached bat.J Neurophysiol. doi:10.1152/jn.00294.2011