Direction-dependent corticofugal modulation of frequency-tuning curves of inferior collicular neurons in the big brown bat, Eptesicus fuscus

2000 ◽  
Vol 186 (10) ◽  
pp. 913-922 ◽  
Author(s):  
Ji Ping Zhang ◽  
Philip H.-S. Jen ◽  
Xinde Sun
Keyword(s):  
Frequency Tuning ◽  
Eptesicus Fuscus ◽  
Tuning Curves ◽  
Big Brown Bat ◽  
Inferior Collicular ◽  
Corticofugal Modulation

scholarly journals Effects of Acetylcholine and Atropine on Plasticity of Central Auditory Neurons Caused by Conditioning in Bats

2001 ◽  
Vol 86 (1) ◽  
pp. 211-225 ◽  
Author(s):  
Weiqing Ji ◽  
Enquan Gao ◽  
Nobuo Suga
Keyword(s):  
Somatosensory Cortex ◽  
Basal Forebrain ◽  
Cortical Neurons ◽  
Frequency Tuning ◽  
Auditory Neurons ◽  
Tuning Curves ◽  
Acoustic Stimuli ◽  
Cholinergic Basal Forebrain ◽  
Big Brown Bat ◽  
Central Auditory Neurons

In the big brown bat ( Eptesicus fuscus), conditioning with acoustic stimuli followed by electric leg-stimulation causes shifts in frequency-tuning curves and best frequencies (hereafter BF shifts) of collicular and cortical neurons, i.e., reorganization of the cochleotopic (frequency) maps in the inferior colliculus (IC) and auditory cortex (AC). The collicular BF shift recovers 180 min after the conditioning, but the cortical BF shift lasts longer than 26 h. The collicular BF shift is not caused by conditioning, as the AC is inactivated during conditioning. Therefore it has been concluded that the collicular BF shift is caused by the corticofugal auditory system. The collicular and cortical BF shifts both are not caused by conditioning as the somatosensory cortex is inactivated during conditioning. Therefore it has been hypothesized that the cortical BF shift is mostly caused by both the subcortical (e.g., collicular) BF shift and the activity of nonauditory systems such as the somatosensory cortex excited by an unconditioned leg-stimulation and the cholinergic basal forebrain. The main aims of our present studies are to examine whether acetylcholine (ACh) applied to the AC augments the collicular and cortical BF shifts caused by the conditioning and whether atropine applied to the AC abolishes the cortical BF shift but not the collicular BF shift, as expected from the preceding hypothesis. In the awake bat, we made the following findings. ACh applied to the AC augments not only the cortical BF shift but also the collicular BF shift through the corticofugal system. Atropine applied to the AC reduces the collicular BF shift and abolishes the cortical BF shift which otherwise would be caused. ACh applied to the IC significantly augments the collicular BF shift but affects the cortical BF shift only slightly. ACh makes the cortical BF shift long-lasting beyond 4 h, but it cannot make the collicular BF shift long-lasting beyond 3 h. Atropine applied to the IC abolishes the collicular BF shift. It reduces the cortical BF shift but does not abolish it. Our findings favor the hypothesis that the BF shifts evoked by the corticofugal system, and an increased ACh level in the AC evoked by the basal forebrain are both necessary to evoke a long-lasting cortical BF shift.

Reorganization of the Frequency Map of the Auditory Cortex Evoked by Cortical Electrical Stimulation in the Big Brown Bat

2000 ◽  
Vol 83 (4) ◽  
pp. 1856-1863 ◽  
Author(s):  
Syed A. Chowdhury ◽  
Nobuo Suga
Keyword(s):  
Electrical Stimulation ◽  
Auditory Cortex ◽  
Cortical Neurons ◽  
Frequency Tuning ◽  
Acoustic Stimulus ◽  
Primary Auditory Cortex ◽  
Neural Representation ◽  
Tuning Curves ◽  
Big Brown Bat ◽  
Frequency Map

In a search phase of echolocation, big brown bats, Eptesicus fuscus, emit biosonar pulses at a rate of 10/s and listen to echoes. When a short acoustic stimulus was repetitively delivered at this rate, the reorganization of the frequency map of the primary auditory cortex took place at and around the neurons tuned to the frequency of the acoustic stimulus. Such reorganization became larger when the acoustic stimulus was paired with electrical stimulation of the cortical neurons tuned to the frequency of the acoustic stimulus. This reorganization was mainly due to the decrease in the best frequencies of the neurons that had best frequencies slightly higher than those of the electrically stimulated cortical neurons or the frequency of the acoustic stimulus. Neurons with best frequencies slightly lower than those of the acoustically and/or electrically stimulated neurons slightly increased their best frequencies. These changes resulted in the over-representation of repetitively delivered acoustic stimulus. Because the over-representation resulted in under-representation of other frequencies, the changes increased the contrast of the neural representation of the acoustic stimulus. Best frequency shifts for over-representation were associated with sharpening of frequency-tuning curves of 25% of the neurons studied. Because of the increases in both the contrast of neural representation and the sharpness of tuning, the over-representation of the acoustic stimulus is accompanied with an improvement of analysis of the acoustic stimulus.

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