Auditory neurons in bats that make use of frequency modulated (FM)

Auditory neurons in bats that make use of frequency modulated (FM) sweeps for echolocation are selective for the behaviorally-relevant prices and direction of frequency modification. For equal strength tones near threshold, LFI is more powerful than HFI. When the inhibitory tone strength is elevated further from threshold, the power asymmetry reduced. The temporal asymmetry in LFI = 9 Streptozotocin enzyme inhibitor bats) anesthetized with isoflurane or methoxyflurane inhalation, accompanied by an i.p. injection of urethane (0.7 mg/g) or pentobarbital sodium (30 g/g). A previous study comparing urethane and barbiturate anesthetics showed no differences in FM sweep selectivity or arrival time/bandwidth of sideband inhibition (Razak and Fuzessery, 2009) Therefore, the data Streptozotocin enzyme inhibitor obtained using the different anesthetics were combined here. To expose the auditory cortex, the head was held in a bite bar, a midline incision was made in the scalp, and the muscles over the dorsal surface of the skull were reflected to the sides. The front of the skull was scraped clean and a layer of glass microbeads applied, followed by a layer of dental cement. The bat was then placed in a Plexiglas holder. A cylindrical aluminium head pin was Rabbit Polyclonal to ATP5S inserted through a cross-bar over the bat’s head and cemented to the previously prepared region of the skull. This pin served to hold the head secure during the recording session. The cross-bar holding the head pin was secured behind the bat, leaving no interference between the speaker and the ear. The location of A1 was decided relative to the rostrocaudal extent of the midsagittal sinus, the distance laterally from the midsagittal sinus, and the location of a prominent lateral blood vessel that lies parallel to the midsagittal sinus. The size of the exposure was usually ~2 mm2. Exposed muscle was covered with petroleum jelly, and exposed brain surface was covered with silicone oil to prevent desiccation. Recording procedures Experiments were conducted in a warm (~80F), sound-proof chamber lined with anechoic foam (Gretch-Ken Industries, Oregon). Bats were kept anesthetized throughout the course of the experiments with additional urethane or pentobarbital sodium (one-third of pre-surgical dose) injections. Acoustic stimulation and data acquisition were driven by custom software and Microstar DSP board based hardware. Programmable attenuators (PA5, Tucker-Davis Technologies, Florida) allowed control of sound intensities before amplification by an integrated amplifier (Yamaha AX430). Stimuli were delivered either using an LCY-K100 ribbon tweeter (Madisound, Wisconsin) placed 8 in from the left ear at 45 to the long-axis of the bat’s body or presented as contralateral ear closed-field stimuli through the ribbon tweeters fitted with funnels. Each neuron reported in this study was tested with one or the other method (free-field or closed-field). Preliminary Streptozotocin enzyme inhibitor data from neurons in which the closed-field and free-field data were compared indicated that the minimum thresholds (MTs) were ~5 dB higher for the free-field presentation. Because all neurons in this study were tested with excitatory tones presented at 10C20 dB above threshold regardless of the presentation method used, it is unlikely that the results were due to the presentation method. Most FM sweep selective neurons tuned between 30C60 kHz in the pallid bat auditory cortex are also binaurally insensitive (EO/O type neurons) when tested with interaural intensity differences (Razak and Fuzessery, 2002). Therefore, IID sensitivity is usually unlikely to create differences between free-field and closed-field data. The frequency response curve of the delivery systems, measured with a 1/4-in microphone (Bruel and Kjaer, Denmark), was flat within 5 dB for frequencies from 6C50 kHz. The roll-off.

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