Neural maps for target range in the auditory cortex of ...raghav/pdfs/animalbehavior/Reading...In...

Neural maps for target range in the auditory cortex ofecholocating batsM Kössl1, JC Hechavarria1, C Voss1, S Macias2, EC Mora2 and M Vater3

Available online at www.sciencedirect.com

ScienceDirect

Computational brain maps as opposed to maps of receptor

surfaces strongly reflect functional neuronal design principles.

In echolocating bats, computational maps are established that

topographically represent the distance of objects. These target

range maps are derived from the temporal delay between

emitted call and returning echo and constitute a regular

representation of time (chronotopy). Basic features of these

maps are innate, and in different bat species the map size and

precision varies. An inherent advantage of target range maps is

the implementation of mechanisms for lateral inhibition and

excitatory feedback. Both can help to focus target ranging

depending on the actual echolocation situation. However,

these maps are not absolutely necessary for bat echolocation

since there are bat species without cortical target-distance

maps, which use alternative ensemble computation

mechanisms.

Addresses1 Institute for Cell Biology and Neuroscience, Goethe University,

Frankfurt, Max-von-Laue-Str. 13, 60439 Frankfurt, Germany2 Department of Animal and Human Biology, Faculty of Biology, Havana

University, calle 25 No. 455 entre J e I, Vedado, CP 10400, Ciudad de La

Habana, Cuba3 Institute for Biochemistry and Biology, University of Potsdam, Karl

Liebknecht Str. 26, 14476 Golm, Germany

Corresponding author: Kössl, M ([email protected])

Current Opinion in Neurobiology 2014, 24:68–75

This review comes from a themed issue on Neural maps

Edited by David Fitzpatrick and Nachum Ulanovsky

For a complete overview see the Issue and the Editorial

Available online 17th September 2013

0959-4388/$ – see front matter, # 2013 Elsevier Ltd. All rightsreserved.

http://dx.doi.org/10.1016/j.conb.2013.08.016

IntroductionSensory brain maps consist of topographically continuousneuronal representations of a certain stimulus feature.Such a representation can already be generated at thesensory surface and either reflects spatially continuoussensory input or properties of sensory filtering along thereceptor surface like the cochlear hair cells. The othertype of map is computational in the sense that it is createdin the brain by extracting behaviourally relevant stimulusinformation [1]. For both types of maps, wiring optimiz-ation and economy regarding projections betweenmapped areas are an inherent advantage. In this sense,a topographically ordered wiring of brain areas should also


require less genetic information than other wiringarrangements [2]. In addition, on a functional level,spatially restricted local neuronal interactions like lateralinhibition can be implemented easily within a spatialparameter gradient as provided by a map [3,4]. Withina map, topological substructures like clusters or pin-wheels can be created to optimize local function [5].As pointed out by Schreiner and Winer [6], map topo-graphies and their connectional metric can also provide astable basis for efficient functional transformations anddynamic remodelling during development, like changinghead related transfer functions during head growth orneuromodulatory control of cortical plasticity [7,8��].

Unlike the visual or somatosensory system where import-ant spatial relationships are already mapped on the re-ceptor surface, spatial auditory information has to becalculated de novo by comparing response properties ofboth ears and in some species is then represented inmidbrain auditory space maps [1]. In the forebrain suchtype of continuous spatial map is no longer prominent andclustered types of representation prevail [e.g. 9]. This isalso true for bat auditory cortex where clustered binauralinteractions [10] and a clustered representation ofdynamic spatial receptive fields could be demonstrated[11]. In the cortex of bats, there are computational mapsthat contain target-relevant information extracted fromreturning echoes [review: 12]. There are two major typesof such maps: first, the delay (D) between emitted bio-sonar signal and returning echo is mapped to derive targetrange (R) with R = D*C/2 (C = sound velocity) (Figure 1).Within such a map individual neurons are most sensitiveto a specific echo delay that is defined as the characteristicdelay (CD). In the mustached bat, Pteronotus parnellii, awidely used bat model for auditory processing, threetarget distance maps have been demonstrated in theFM-FM, dorsal fringe and ventral fringe (DF, VF) cor-tical areas, respectively [13��,14–16], second, relativevelocity between bat and object is mapped in form ofDoppler-induced echo frequency shifts [17]. In contrastto any other receptor-surface-dominated or compu-tational map, input into these maps is actively controlledby the animal through its echolocation signal emission.

Chronotopic target range maps in differentbat speciesTarget range maps were initially discovered by Suga,O’Neill and colleagues in the auditory cortex of themustached bat P. parnellii by using passive auditorystimulation with pairs of frequency modulated (FM)

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Target range maps in echolocating bats Kössl et al. 69

Figure 1

R = D*C/2

R = target rangeD = echo delayC = sound velocity

call

echo

Current Opinion in Neurobiology

Echolocating bat that computes target range (R) from the echo delay (D).

sweeps that mimic the FM components of echolocationsignal and echo. Neurons that preferentially respond to aspecific echo delay (Figure 2: examples of delay tuningcurves from different bat species) are arranged in approxi-mately rostrocaudal direction such that neurons respond-ing to short echo delay and hence short target distancesare represented more rostrally than neurons responding tolong echo delays (Figure 3). The mustached bat is a new

Figure 2

P. parnellii

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Examples of receptive fields of delay-sensitive neurons in 3 bat species: P. pa

of FM sweeps separated by a specific delay that represents sonar pulse and e

delay are varied. Normalized neuronal response strength is color coded, red

50% of maximal activity. The response area can be echo level invariant (a,c

approaching objects on a single neuron basis (see text).


world long-CF–FM bat where the FM component whichis important for target range estimation is preceded by aconstant frequency (CF) component that is used by thebat to exploit echo Doppler-shifts to derive informationon relative velocity. Velocity sensitive neurons are alsoarranged in form of a computational map (P. parnellii: CF–CF area, see Figure 3; [17]). Remarkably, chronotopy hasevolved convergently both in old and new world batfamilies. Rhinolophus rouxi, a bat species from the familyRhinolophidae that is widely distributed in the old worldpossesses a target range map located in the dorsal auditorycortex ([18], Figure 3). However, in the auditory cortex ofbats, that only employ FM biosonar signals, delay sensi-tive neurons are not necessarily arranged in form of targetdistance maps [19,20��,21]. In Eptesicus fuscus they formclusters that are located mainly within a high frequencycortex region where cortical tonotopy reverses ([21];Figure 3). Only recently were target maps discoveredfor a frugivorous FM bat, Carollia perspicillata [22��] andfor the insectivorous short-CF–FM bat Pteronotus quad-ridens [23�]. Interestingly, in C. perspicillata, delay-sensi-tive neurons occur in dorsal high frequency areas andwithin a region where tonotopy reverses in primary audi-tory cortex, as in E. fuscus (Figure 3).

It is still open if the presence of a short or long CFcomponent in the echolocation signal and the accompa-nying added cortical computational complexityencourages the formation of a mapped target range pro-

elay [ms]

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adridens C. perspicillata


rnellii, P. quadridens, and C. perspicillata. The stimulus consists of a pair

cho. The call level is held constant at 70 or 80 dB SPL, the echo level and

indicates maximal number of action potentials, the black line indicates

,e) or tilted (b,d,f). Tilt can provide for a certain amount of tracking of


70 Neural maps

Figure 3

Rhinolophus rouxi FM-FM

FM-FM

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Myotis lucifugus

Eptesicus fuscus

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Current Opinion in Neurobiology 2014, 24:68–75 www.sciencedirect.com


cessing area. However, the FM bat C. perspicillata hasimplemented a prominent target range map in the cortex.There are no CF components in the call of C. perspicillata(Figure 3). This could suggest that chronotopy is a verybasic feature at the root of the evolutionary tree of thesister groups of Phyllostomatidae, to which C. perspicillatabelongs, and the Mormoopidae with the genus Pteronotus[see 23�]. This hypothesis is strengthened by the pre-sence of chronotopic cortex organization in other phyl-lostomids [24�].

Generation of cortical chronotopyIn bat species that have cortical chronotopy, the gener-ation of echo delay maps takes place through spatialsorting, and hence transformation of neuronal projectionsfrom inferior colliculus (where there is no map, see below)to auditory thalamus and cortex.

The building blocks of cortical chronotopic maps aredelay-sensitive neuronal interactions occurring at subcor-tical levels. For P. parnellii it has been demonstrated thatfacilitatory delay-sensitivity in the ascending auditorysystem first emerges at the level of the central nucleusof the inferior colliculus (ICc; [25,26, review: 27��]).Paradoxically, the main components of creation of facil-itatory delay-sensitivity in ICc are glycinergic inputs[28,27��]. In addition, the ICc inherits a delay-tunedinhibition from the intermediate nucleus of the laterallemniscus (INLL), conveyed via an excitatory glutami-nergic input [28–32]. Within the ICc, delay tuned neuronsare integrated in the tonotopic representation and are notarranged according to CD [33], and they also can be tunedto sound duration [34]. The tectothalamic projectioncreates spatially discrete assemblies of delay-tunedneurons in two regions of the rostral half of the medialgeniculate body (MGB) that are organized according toharmonic frequency bands (FM2, 3, 4). Furthermore,there is a crude representation of characteristic delay inMGB [35, for further references see 27��].

Thalamocortical projections feed three discrete rangingareas in AC of P. parnellii. The FM-FM-area and the VFreceive overlapping projections from rostral MGB derivedmainly from lateral parts, whereas the DF receives inputfrom medial parts [36]. Since there are massive cortico-thalamic backprojections, the cortex could also imprint itschronotopic organization onto its main input structure. Sofar, specific functional roles have not been assigned to themultiple delay representations.

Figure 3 Legend Target range maps in different bat species. Left: represent

position of auditory cortex. Right: detailed view of chronotopic maps within

give direction of representation of decreasing echo delay. Black arrows indi

that in E. fuscus and M. lucifugus, delay-sensitive neurons are not arranged

Cortex data are from Schuller et al. [18], Suga [12], Hechavarria et al. [23�], Ha

rouxi were kindly provided by D. Leipert, calls for M. lucifugus by B. Fenton


Emergent features within target distancemapsNeural processing to create delay tuning in P. parnelliiappears largely complete at subcortical levels. The sharp-ness of delay tuning (50% width) is similar in IC, MGBand AC [15,26,35,37]. Furthermore, the range of CDs issimilar in IC, MGB, and AC with an overrepresentation ofdelays from 1 to 10 ms [15,26].

Cortical delay-tuned responses, on the other handhave certain response features and show interactionsthat are not yet present at lower levels and could havebeen implemented with the help of a chronotopicgradient:� Among those are a higher specificity regarding stimulus

type in P. parnellii for FM stimulus pairs and lessresponsiveness to single FM components or to puretone stimuli than in the IC and MGB [14,27��,37,38].However, in this respect cortical delay-tuned neuronsin C. perspicillata are clearly less specific and they allrespond vigorously to single pure tones [39�].

� Mechanisms of lateral inhibition and excitatoryfeedback that sharpen or shift response tuning areone of the major advantages of a map, and could beused to provide dynamic plasticity of receptive fieldsduring learning or arousal [40]. There is ampleevidence from the work of Suga and colleagues onplasticity of neuronal tuning both in tonotopic and intarget range sensitive cortical areas in P. parnellii.They showed that a combination of widespread lateralinhibition in the cortex and highly focused excitatoryfeedback via projections to other cortical or sub-cortical areas creates a self-organizing map [8��,41].Cortical neurons within this map that code beha-viourally important stimuli, can augment the activityof neurons with a similar, ‘matched’ CD in the targetarea and also recruit additional neurons while activityof unmatched neurons is reduced. For the intra-cortical interaction between the 3 target distancemaps, this type of ‘egocentric selection’ has beendemonstrated by local cortical electrical activation[42–45]: The FM-FM area predominantly maintainsa strong suppressive influence on unmatchedneurons in the other two areas and on thecontralateral FM-FM area. This suppression canalso result in a shift of the CD of the unmatchedneurons away from the CD of the FM-FM neuron(centrifugal CD shift). In contrast, the DF and VFareas have a mostly augmenting influence onmatched neurons in the FM-FM area. This can

ative spectrograms of echolocation calls. Middle: brain overview with the

auditory cortex. Target range computing areas are in blue, white arrows

cate increasing characteristic frequency in tonotopic areas. Please note

in a chrontopic map but are interspersed within the tonotopic cortex.

gemann et al. [22��], Dear et al. [21], Wong and Shannon [19]. Calls for R.

, calls from E. fuscus by M. Gadziola.


72 Neural maps

shift the CD of matched neurons closer to the CD ofthe DF or VF neuron (centripetal CD shift). Thelatter could produce a focussing on and sharpeningof tuning to short echo delays in the FM-FM area,since the mapped delay range in DF and VF isrestricted to shorter delays in comparison to the FM-FM area [see 8��].This form of self-organizing feedback interaction is aquite powerful general neuronal organization principleand is also found in the interaction between cortex andICc and MGB [46,47]. In general, the dominance ofcentrifugal plasticity could shape the selective neuralrepresentation of a specific target distance and producecontrast enhancement. Dominance of centripetalactions could result in strong clustering and expandthe representation of a selected specific targetdistance.

� In P. parnellii, P. quadridens, and C. perspicillata, asubstantial proportion of cortical delay-tunedneurons, in particular those responding to longerdelays at threshold have a tilted receptive field thatcould allow a certain degree of target tracking(Figure 2, [39�,23�]). When the bat approaches itstarget, echo intensity increases due to decreasingtarget-range. As a consequence, during the end stageof approach, only those neurons with appropriatelytilted receptive field will continue to respond tolouder echoes at shorter delays. In this respect tiltedreceptive fields loose specificity in terms of staticobject distance but gain specificity in terms ofresponding to echo series that are typical for approachto target — and may facilitate target tracking. We notethat some bat species reduce call intensity [48], andthen this sort of tracking at the level of individualneurons would not work. For P. parnellii tiltedresponse areas are present in the FM-FM area butare not found in the IC [49�]. They could be generatedwithin the topographic gradient of the map if there is alevel-dependent asymmetry of input convergence orinput integration in cortical neurons.

� Map topography could also provide a more effectivemeans to exert local and delay-specific gain regulationby modulation through local GABAergic interneuronsor external modulatory systems.

� Additional parameter representation: A 2D repres-entation of a single parameter (echo delay) in principleallows arranging additional axes orthogonal to the mapto represent/process other features. In the FM-FM andDF areas of P. parnellii, the three relevant frequencybands of the echo harmonics (FM2, 3, 4) are separatedand projected orthogonal to the delay axis [14,15]. Sucha harmonic dissociation is not found in P. quadridens orC. perspicillata and in R. rouxi there are no relevantmultiple harmonics in the echo.

� Chronotopic maps could also serve non-target relevantpurposes: In P. parnellii, neurons in the FM-FM areanot only respond well to FM pulse-echo pairs of


specific delay but also to the specific temporal syntax ofsyllables within communication sounds [50,51].

Chronotopic maps as interface to spatial-memory, decision-making, and motor-controlsystems?Chronotopic maps of target distance that, depending onthe echolocation situation, plastically adjust to mostrelevant input features (see above) could also providean efficient interface to other cortical processing systems.Completely unknown is the transfer of spatial infor-mation from target distance maps to hippocampal placecells that in bats have features comparable to those inrodents [52,53��].

A chronotopically organized target distance representa-tion could provide an efficient interface to the motorsystem, in particular since there are target-distancespecific behaviours. Most notable is the switch fromlow call repetition rates during the approach phase ofecholocation to high call repetition rates in the finalphase shortly before the insect is caught. The wingcontrol breaking behaviour close to obstacles (alarmhypothesis, [18]) is also target-distance specific. Bothtypes of behaviour should be triggerable by short echodelays, and the above mentioned intracortical positivefeedback systems that enhance activity to short echodelays may be especially efficient for inducing thosebehaviours. There are also specific reactions to conspe-cifics if they fly close by [54].

A chronotopic representation may also offer advantagesfor efficient input from decision-making systems. Theneurons in the FM-FM area that respond both tocall-echo pairs of specific delay and to complex communi-cation signals may have input from auditory regions offrontal cortex [55,56]. It is still to be tested if frontal cortexcould initiate a switching between both processing modesin the FM-FM area.

But how are bats without target-distancemaps coping?In two insectivorous bat species that exclusively use FMecholocation signals and that predominantly hunt in openuncluttered space, target distance maps have not beendemonstrated. In E. fuscus (Figure 3) delay-sensitiveneurons are clustered mainly between two tonotopic areasand are interspersed with neurons sensitive to single puretones. In M. lucifugus the cortical location of those neuronsoverlaps with tonotopically arranged neurons. Theabsence of a delay map in E. fuscus has inspired research-ers to develop an alternative model for cortical repres-entation of target distance and acoustic scenes based onensemble coding over a larger number of neurons[20��,57,58��,59��]. It also has been demonstrated thatthe population of cortical neurons tuned to echo-delaycould integrate information from objects with different



space-depths for the formation of acoustic images. Thelatter mechanism can manage a quite powerful processingof realistic echolocation call/echo sequences [59��] and itcould also be present in the cortex of bat species that havea delay map [60]. Therefore, at present there is still anopen discussion if delay maps are strictly necessary forefficient extraction of spatial target distance informationor if important features of such a processing also could beobtained by other cortical mechanisms.

Innate cortical chronotopy in batsSharply tuned delay-sensitive cortical neurons arealready present in neonate P. parnellii and C. perspicil-lata, and their topography is comparable to those of adultmaps [61��]. In particular the neurons tuned to shortecho delay have receptive fields that are quite similar tothose of adults. In this respect the delay-tuned dorsalauditory cortex matures earlier than the tonotopicprimary auditory cortex [62]. The establishment ofthose first basic maps of target distance takes placewithout prior experience since the young bats do notyet echolocate [63,64] and therefore the maps seem tobe hardwired in early prenatal developmental stages. Ofcourse we expect that during ongoing postnatal devel-opment the above described feedback mechanismsexert a fine-tuning and adaptation of certain featuresof delay-tuned neurons. However, basic implementa-tion of target-distance sensitive neurons and maps isprobably of high evolutionary value such that a prewir-ing that is genetically determined takes place. It isnoteworthy that the a priori implementation of activespace perception in bats has its complement in passivespace perception: in young rodents, head-direction cellsand hippocampal place cells are already implementedbefore their first use [65,66].

ConclusionActive space perception by means of echo-delay tunedneurons is essential for echolocating bats. In manyspecies, these neurons are arranged in cortical mapsthat possess a rather unique chronotopic neuronalrepresentation. Basic features of such target-distancemaps are innate and most probably hardwired. This apriori implementation of spatial perception emphasizestheir behavioural relevance for bats. Importantly, oncetarget-distance maps are established they seem to beconserved during evolution of bat families and theywere implemented at least two times independentlyin convergent evolution in old and new world bats.However, the functional relevance of such maps is stilldiscussed since there are other coding principles thatcould extract echo delay information from auditoryscenes. In addition, an ordered time representation onthe cortical surface could also be exploited for extractingsignal features that are not related to echolocation but tocommunication.


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� of special interest�� of outstanding interest

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Classic paper on neuronal computations that serve auditory sceneanalysis without the use of target distance maps.

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Hagemann C, Esser KH, Kössl M: A chronotopically organizedtarget distance map in the auditory cortex of the short-tailedfruit bat. J Neurophysiol 2010, 103:222-333.

Discovery of delay sensitive neurons and a large target-distance map in abat species that is not specialized for insect hunting but is frugivorous.

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Hechavarria JC, Macias S, Vater M, Mora EC, Kössl M: Evolutionof neuronal mechanisms for echolocation: specializations fortarget-range computation in bats of the genus Pteronotus. JAcoust Soc Am 2013, 133:570-578.

The FM-bat P. quadridens uses heteroharmonic echolocation and cor-tical target distance maps just like its relative, the CF–FM bat P. parnellii.This suggests that target-distance maps and heteroharmonic echoloca-tion could have been subjected to positive Darwinian selection in theevolution of bats.

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Binaural presentation of semi-natural echo sequences demonstrates thatdelay-sensitive cortical neurons are involved in extraction of direction anddistance of objects.

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26. Portfors CV, Wenstrup JJ: Delay-tuned neurons in the inferiorcolliculus of the mustached bat: implications for analyses oftarget distance. J Neurophysiol 1999, 82:1326-1338.

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Wenstrup JJ, Portfors CV: Neural processing of target distanceby echolocating bats: functional roles of the auditorymidbrain. Neurosci Biobehav Rev 2011, 35:2073-2083.

Delay tuning but not chronotopy is created in the midbrain. This reviewgives comprehensive insight into cellular mechanisms and discussesrelevant processing strategies for generation of delay tuning.

28. Sanchez J, Gans D, Wenstrup JJ: Glycinergic ‘inhibition’mediates selective excitatory response to combinations ofsounds. J Neurosci 2008, 28:80-90.

29. Portfors CV, Wenstrup JJ: Responses to combinations of tonesin the nuclei of the lateral lemniscus. J Assoc Res Otolaryngol2001, 2:104-117.

30. Peterson DC, Nataraj K, Wenstrup JJ: Glycinergic inhibitioncreates a form of spectral integration in nuclei of the laterallemniscus. J Neurophysiol 2009, 102:1004-1016.

31. Peterson DC, Voytenko S, Gans D, Galazyuk A, Wenstrup JJ:Intracellular recordings from combination-sensitive neuronsin the inferior colliculus. J Neurophysiol 2008, 100:629-634.

32. Yavuzoglu A, Schofield BR, Wenstrup JJ: Substrates of auditoryfrequency integration in a nucleus of the lateral lemniscus.Neuroscience 2010, 169:906-919.

33. Portfors CV, Wenstrup JJ: Topographical distribution of delay-tuned responses in the mustached bat inferior colliculus. HearRes 2001, 151:95-105.

34. Macias S, Hechavarria JC, Kössl M, Mora EC: Neurons in theinferior colliculus of the mustached bat are tuned both toecho-delay and sound duration. Neuroreport 2013, 24:404-409.

35. Wenstrup JJ: Frequency organization and responses tocomplex sounds in the medial geniculate body of themustached bat. J Neurophysiol 1999, 82:2528-2544.

36. Pearson JM, Crocker WD, Fitzpatrick DC: Connections offunctional areas in the mustached bat’s auditory cortex withthe auditory thalamus. J Comp Neurol 2007, 500:401-418.

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Receptive fields of delay-sensitive neurons are remarkably similarbetween insectivorous and frugivorous bat species.

40. Weinberger NM: Dynamic regulation of receptive fields andmaps in the adult sensory cortex. Annu Rev Neurosci 1995,18:129-158.

41. Suga N, Yan J, Zhang Y: Cortical maps for hearing and egocentricselection for self-organization. Trends Cog Sci 1997, 1:13-20.

42. Xiao Z, Suga N: Reorganization of the auditory cortexspecialized for echo-delay processing in the mustached bat.Proc Natl Acad Sci USA 2004, 101:1769-1774.

43. Tang J, Suga N: Modulation of auditory processing by cortico-cortical feed-forward and feedback projections. Proc NatlAcad Sci USA 2008, 105:7600-7605.

44. Tang J, Suga N: Corticocortical interactions between andwithin three cortical auditory areas specialized for time-domain signal processing. J Neurosci 2009, 29:7230-7237.

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47. Yan J, Suga N: Corticofugal amplification of facilitativeauditory responses of subcortical combination-sensitiveneurons in the mustached bat. J Neurophysiol 1999, 81:817-824.

48. Hiryu S, Shiori Y, Hosokawa T, Riquimaroux H, Watanabe Y: On-board telemetry of emitted sounds from free-flying bats:compensation for velocity and distance stabilizes echofrequency and amplitude. J Comp Physiol A 2008, 194:841-851.

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Macias S, Mora EC, Hechavarrı́a JC, Kössl M: Properties of echodelay-tuning receptive fields in the inferior colliculus of themustached bat. Hear Res 2012, 286:1-8.

Comparison of echo delay sensitive neurons between midbrain andcortex in P. parnellii.

50. Esser K-H, Condon CJ, Suga N, Kanwal JS: Syntax processingby auditory cortical neurons in the FM–FM area of themustached bat Pteronotus parnellii. Proc Natl Acad Sci USA1997, 94:14019-14024.

51. Kanwal JS, Rauschecker JP: Auditory cortex of bats andprimates: managing species-specific calls for socialcommunication. Front Biosci 2007, 12:4621-4640.

52. Ulanovsky N, Moss CF: Hippocampal cellular and networkactivity in freely moving echolocating bats. Nat Neurosci 2007,10:224-233.

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Ulanovsky N, Moss CF: Dynamics of hippocampal spatialrepresentation in echolocating bats. Hippocampus 2011,21:150-161.

Evidence that bats possess space-sensitive neurons in the hippocampus.The data show how spatial representation depends on echolocationbehavior and exploratory modes.

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Neural maps for target range in the auditory cortex of echolocating batsIntroductionChronotopic target range maps in different bat speciesGeneration of cortical chronotopyEmergent features within target distance mapsChronotopic maps as interface to spatial-memory, decision-making, and motor-control systems?But how are bats without target-distance maps coping?Innate cortical chronotopy in batsConclusionReferences and recommended reading

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