Editing Animal echolocation (section)

===== Auditory cortex =====

The [[auditory cortex]] in bats is quite large in comparison with other mammals.<ref>{{cite journal |last1=Kanwal |first1=Jagmeet S. |last2=Rauschecker |first2=J. P. |title=Auditory cortex of bats and primates: managing species-specific calls for social communication |journal=Frontiers in Bioscience |volume=12 |issue=8–12 |pages=4621–4640 |date=May 2007 |pmid=17485400 |pmc=4276140 |doi=10.2741/2413 }}</ref> Various characteristics of sound are processed by different regions of the cortex, each providing different information about the location or movement of a target object. Most of the existing studies on information processing in the auditory cortex of the bat have been done by [[Nobuo Suga]] on the mustached bat, ''[[Pteronotus parnellii]]''. This bat's call has both CF tone and FM sweep components.<ref name="Suga 1975"/><ref name="Suga 1987"/>

Suga and his colleagues have shown that the cortex contains a series of "maps" of auditory information, each of which is organized systematically based on characteristics of sound such as [[frequency]] and [[amplitude]]. The neurons in these areas respond only to a specific combination of frequency and timing (sound-echo delay), and are known as combination-sensitive neurons.<ref name="Suga 1975"/><ref name="Suga 1987"/>

The systematically organized maps in the auditory cortex respond to various aspects of the echo signal, such as its delay and its velocity. These regions are composed of "combination sensitive" neurons that require at least two specific stimuli to elicit a response. The neurons vary systematically across the maps, which are organized by acoustic features of the sound and can be two dimensional. The different features of the call and its echo are used by the bat to determine important characteristics of their prey. The maps include:<ref name="Suga 1975"/><ref name="Suga 1987"/>

[[File:Bat Auditory Cortex.svg|thumb|upright=1.2|Auditory cortex of a bat
{{legend |#BA54C0 |FM-FM area |text=A |textcolor=white}}
{{legend |#4190B9 |CF-CF area |text=B |textcolor=white}}
{{legend |#4AB8B6 |Amplitude-sensitive area |text=C |textcolor=white}}
{{legend |#DC7A5B |Frequency-sensitive area |text=D |textcolor=white}}
{{legend |#90C675 |DSCF area |text=E |textcolor=white}}]]

*'''FM-FM area''': This region of the cortex contains FM-FM combination-sensitive neurons. These cells respond only to the combination of two FM sweeps: a call and its echo. The neurons in the FM-FM region are often referred to as "delay-tuned", since each responds to a specific time delay between the original call and the echo, in order to find the distance from the target object (the range). Each neuron also shows specificity for one harmonic in the original call and a different harmonic in the echo. The neurons within the FM-FM area of the cortex of ''Pteronotus'' are organized into columns, in which the delay time is constant vertically but increases across the horizontal plane. The result is that range is encoded by location on the cortex, and increases systematically across the FM-FM area.<!--<ref name="Neuweiler_2003"/><ref name="Carew_2001"/>--><ref name="Suga 1975">{{cite journal |last1=Suga |first1=N. |last2=Simmons |first2=J. A. |last3=Jen |first3=P. H. |year=1975 |title=Peripheral specialization for fine analysis of doppler-shifted echoes in the auditory system of the "CF-FM" bat Pteronotus parnellii | journal=Journal of Experimental Biology |volume=63 |issue=1 | pages=161–192 |doi=10.1242/jeb.63.1.161 |pmid=1159359 }}</ref><ref>{{cite journal |last1=Suga |first1=N. |last2=O'Neill |first2=W. E. |s2cid=11840108 |title=Neural axis representing target range in the auditory cortex of the mustache bat |journal=Science |volume=206 |issue=4416 |pages=351–353 |date=October 1979 |pmid=482944 |doi=10.1126/science.482944 |bibcode=1979Sci...206..351S }} </ref>
*'''CF-CF area''': Another kind of combination-sensitive neuron is the CF-CF neuron. These respond best to the combination of a CF call containing two given frequencies – a call at 30&nbsp;kHz (CF1) and one of its additional [[harmonics]] around 60 or 90&nbsp;kHz (CF2 or CF3) – and the corresponding echoes. Thus, within the CF-CF region, the changes in echo frequency caused by the [[Doppler shift]] can be compared to the frequency of the original call to calculate the bat's velocity relative to its target object. As in the FM-FM area, information is encoded by its location within the map-like organization of the region. The CF-CF area is first split into the distinct CF1-CF2 and CF1-CF3 areas. Within each area, the CF1 frequency is organized on an axis, perpendicular to the CF2 or CF3 frequency axis. In the resulting grid, each neuron codes for a certain combination of frequencies that is indicative of a specific velocity<ref name="Carew_2001"/><ref name="Suga 1975"/><ref name="Suga 1987">{{cite journal |last1=Suga |first1=N. |last2=Niwa |first2=H. |last3=Taniguchi |first3=I. |last4=Margoliash |first4=D. |s2cid=18390219 |title=The personalized auditory cortex of the mustached bat: adaptation for echolocation |journal=Journal of Neurophysiology |volume=58 |issue=4 |pages=643–654 |date=October 1987 |pmid=3681389 |doi=10.1152/jn.1987.58.4.643 }}</ref>
*'''Doppler shifted constant frequency (DSCF) area''': This large section of the cortex is a map of the acoustic fovea, organized by frequency and by amplitude. Neurons in this region respond to CF signals that have been Doppler shifted (in other words, echoes only) and are within the same narrow frequency range to which the acoustic fovea responds. For ''Pteronotus'', this is around 61&nbsp;kHz. This area is organized into columns, which are arranged radially based on frequency. Within a column, each neuron responds to a specific combination of frequency and amplitude. This brain region is necessary for frequency discrimination.<ref name="Carew_2001"/><ref name="Suga 1975"/><ref name="Suga 1987"/>