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H Scheich

Publications and source records attributed to H Scheich.

At least 73 records · Page 4Linked to original sources
PubMed1996

Ultrastructural localization of glycogen phosphorylase predominantly in astrocytes of the gerbil brain.

The localization of glycogen phosphorylase in gerbil brain was determined by immunoelectron microscopy using the pre-embedding peroxidase technique. Electron-dense granular reaction product of peroxidase activity was observed in astrocytes of all brain regions examined (cerebral cortex, striatum, cerebellar cortex, hippocampal formation, corpus callosum, mesencephalic trigeminal nucleus). The reaction product was distributed in a diffuse pattern throughout the cytoplasmic matrix of perikarya and processes; sometimes the nucleus of labeled astrocytes also contains immunopositive material. The light microscopically visible glycogen phosphorylase immunoreactivity associated with capillaries could be characterized as a staining of astrocytic endfeet ensheathing capillaries. Endothelial cells and pericytes were never labeled. In addition to astrocytes, ependymal cells also presented immunopositive material in their cytoplasm. On the other hand, no reaction product was observed in cells identified as oligodendroglia or microglia. Neurons (with the exception of neurons of the mesencephalic trigeminal nucleus), their processes, and their synaptic endings were free of reaction product. In the neuropil we frequently observed immunopositive glial processes adjacent to synaptic structures. This intimate spatial relationship may be interpreted as a morphological sign of a metabolic interaction. The data support the hypothesis that astroglia play a key role in glycogen metabolism and energization of the brain.

Animals↗
PubMed1996

Alteration of auditory cortex activity with a visual stimulus through conditioning: a 2-deoxyglucose analysis.

In two experiments, the 2-deoxyglucose metabolic mapping technique was used to examine the hypothesis that a stimulus of one modality (a light) will begin to activate the sensory cortex of a stimulus of another modality (a tone) with which it has been repeatedly paired. Adult gerbils received repeated presentations of either a light or the light paired with a tone known to affect 2DG labeling patterns in the auditory cortex. Intermittent footshock was included on a pseudo-random basis to maintain arousal in the subjects. One day after training, each gerbil was injected with 2DG and either received repeated presentations of the light only or was simply exposed to the training context. Analysis of the auditory cortex revealed no differences in overall metabolic activity of the auditory cortex between the groups. However, in both experiments, the light that was previously paired with the tone changed the relative activity of the cortical subfields compared to the light not previously paired with the tone. Specifically, the results indicate greater activity in the anterior auditory field (AAF-Experiments 1 and 2) and the posterior fields (DPVP-Experiment 2) relative to the primary field AI in response to the light that was previously paired with the tone during training. Gerbils either only placed in the context during the 2DG session or that received unpaired presentations of the light and tone during training did not show this shift in relative labeling between the subfields. Because no differences in overall activity of the auditory cortex were found, we conclude that the shift in relative labeling between the subfields reflects, on average, both an increase in activity of fields AAF and DPVP and a concomitant decrease in AI activity in response to the light stimulus. The results have implications for our understanding both of brain learning mechanisms in general and the potential functions of auditory cortex subfields in particular.

Animals↗
PubMed1996

Differential frequency conditioning enhances spectral contrast sensitivity of units in auditory cortex (field Al) of the alert Mongolian gerbil.

Differential aversive auditory conditioning in the awake Mongolian gerbil was performed during single- and multi-unit recording in field Al of the primary auditory cortex. Presentations of pure tone stimuli of a given frequency (reinforced conditioned stimulus; CS+) paired with electrocutaneous stimulation (unconditioned stimulus) were combined with several other non-reinforced tone stimuli (non-reinforced conditioned stimulus; CS-). Stimulus presentation during training and testing was optimized for constancy of the probability of occurrence of both the CS+ and the CS- stimulus. The paradigm led to a reorganization of both the spectral and temporal response characteristics of auditory cortical neurons with the following basic results. First, tone-evoked responses of Al neurons recorded after multiple acoustic stimulation under these conditions varied statistically around a mean value (stationarity). Conditioning produced a shift in mean values of evoked responses. The altered tone responses were also stationary (stability of the plastic effects). Second, the frequency-receptive fields (FRFs) of neurons were reorganized in a frequency-specific way such that the CS+ frequency became located in a local minimum of the FRF after training. This resulted from a training-induced increase in the responses to frequencies adjacent to the CS+ frequency in the FRF relative to the CS+ response. The effect can be interpreted as an enhancement of the 'spectral contrast' sensitivity of the unit in the CS+ neighbourhood. Third, apart from this frequency-specific plastic effect, responses to other frequencies also underwent changes during training. The non-frequency-specific changes were not generally predictable but the post-trial responses were stationary. Fourth, the analysis of the long-term behaviour of FRF reorganization revealed the stability of plastic effects under retention training and the gradual re-establishment of the pretrial FRF during extinction training. Fifth, not only the spectral characteristics but also the temporal structure of the tone-evoked responses could be affected by the training. In most cases the training-induced changes measured within the first tens of milliseconds of the response corresponded to the response changes obtained by integration over the total response period. There were some cases, however, in which the direction of the response change varied with time, indicating that excitatory and inhibitory influences on the temporal response pattern were differently affected by training.

Acoustic Stimulation↗
PubMed1995

Comparison of frequency-specific c-Fos expression and fluoro-2-deoxyglucose uptake in auditory cortex of gerbils (Meriones unguiculatus).

Induction of c-Fos in the auditory cortex of gerbils was investigated immunocytochemically 1 h after single, triple or 1 h continuous stimulation with a series of narrow band frequency-modulated tone bursts. With single stimulation c-Fos immunoreactive neurons were chiefly found in the primary auditory field (AI), where they formed a narrow frequency-specific column across layers II-VI. Side-band-like patterns adjacent to this column appeared characteristically with triple stimulation. Immunoreactive cell density in the anterior auditory field and the caudal fields was sparse and location not frequency specific with single or triple stimulation. Spatial comparisons of c-Fos immunoreactive neuron density with 2-deoxy-2-fluoro-D-glucose (FDG) autoradiography in the same animals after 1 h of stimulation revealed spreading of c-Fos expression in neurons across the tonotopic maps of the AI and in the rostral and caudal fields of the auditory cortex. The pattern of the highest density of c-Fos labelled cells in the AI still matched the peak labelling of FDG autoradiographs. The results show that the postsynaptic marker c-Fos reflects the frequency representation in the AI with single or triple stimulation yet with a higher spatial resolution than the deoxyglucose technique. Longer stimulation causes nontonotopic intracortical spreading of the c-Fos-inducing message, a phenomenon potentially reflecting the effects of cooperativity in the maps.

Animals↗
PubMed1995

Mapping of stimulus features and meaning in gerbil auditory cortex with 2-deoxyglucose and c-Fos antibodies.

The basic functional organization of gerbil auditory cortex was previously mapped with unit recording of best frequency and with the fluoro-2-deoxyglucose mapping (FDG) technique. Among at least seven subfields in this cortex the primary auditory cortex (AI) and the anterior auditory field (AAF) showed prominent tonotopic organization with parallel dorsoventral iso-frequency contours (electrophysiology) in correspondence to FDG labelling of frequency band laminae. In an approach to mechanisms of learning aversive tone conditioning paradigms were found to reshape frequency receptive fields of single units in AI and also produced spatial shifts of tone representation in the tonotopic maps of AI and AAF. Both results suggest that spectral features as well as aspects of behavioural meaning of sounds may be represented even in primary auditory cortex. General meaningfulness in terms of occurrence of novel and salient stimuli may be reflected by expression of immediate early genes. Mapping with an antibody against the immediate early gene product c-Fos was performed in order to identify the spatial distribution of neurons in auditory cortex which change metabolism as a result of stimulation with auditory signals in a new environment. Very short e.g. less than 3 min repetitive stimulation with a tone led to frequency-specific columnar expression of c-Fos in AI and to spare non-tonotopic expression in other fields. Longer stimulation or longer aversive conditioning with the same tone led to spreading of expression, i.e. to accessory non-tonotopic labelling in AI and other fields, particularly pronounced in the output layers V and VI. It is assumed that this spreading relates to the formation of output schemes from auditory cortex in terms of implicit behavioural meaning of stimuli.

Animals↗
PubMed1994

Synaptic potentiation and depression in slices of mediorostral neostriatum-hyperstriatum complex, an auditory imprinting-relevant area in chick forebrain.

Long-term potentiation, a tetanic stimulation-evoked, persistent increase in synaptic efficiency, is the most extensively studied form of synaptic plasticity. Intracellular correlates of long-term potentiation have been analysed in mammalian hippocampus and cortex, but not in bird cortical analogues. We present here studies on long-term potentiation in slices of the chick forebrain area mediorostral neostriatum-hyperstriatum complex which receives thalamic afferents and is relevant for auditory filial imprinting. Following afferent tetanic stimulation, population spike potentiation was extracellularly recorded in 25% of the tested neurons for longer than 40 min. Using intracellular recordings, the membrane potential, the amplitude of excitatory postsynaptic potentials, the latency between the test stimulus and the evoked action potentials, and the cellular excitability (excitatory postsynaptic potential-spike relationship) were found to change after the tetanus. A long-term depression following the tetanus was also seen in some units in this area. Furthermore, the mechanisms underlying long-term potentiation were investigated. A large depolarization of resting membrane potential (approx. 36 mV) was characteristic after the tetanic stimulation. N-methyl-D-aspartate receptor channels are necessary for induction of this depolarization, as well as for long-term potentiation, as demonstrated by the effect of DL-2-amino-5-phosphonovaleric acid. After intracellular recordings, the cells were injected with Lucifer Yellow. The combination of electrophysiological characterization and morphological identification suggested that the potentiation came chiefly from type I neurons, which have the largest soma among the neuron types in this area and up to eight dendrites. The results demonstrate that the recognized major phenomena of long-term potentiation are found in an auditory imprinting-relevant area of the chick forebrain, and that this potentiation is dependent on N-methyl-D-aspartate receptor channels. It is noteworthy that behavioural imprinting was previously shown to induce a reduction of up to 47% of the spine frequency of type I neurons and a growth of the remaining spine synapses, all resembling a synaptic selection process. Therefore, the intriguing possibility emerges that mechanisms underlying long-term potentiation are instrumental for this selection process, which involves regressive and proliferative morphological changes.

Acoustic Stimulation↗
PubMed1993

Functional organization of auditory cortex in the mongolian gerbil (Meriones unguiculatus). I. Electrophysiological mapping of frequency representation and distinction of fields.

The frequency representation within the auditory cortex of the anaesthetized Mongolian gerbil (Meriones unguiculatus) was studied using standard microelectrode (essentially multiunit) mapping techniques. A large tonotopically organized primary auditory field (AI) was identified. High best frequencies (BFs) were represented rostrally and low BFs caudally along roughly dorsoventrally oriented isofrequency contours. Additional tonotopic representations were found adjacent to AI. Rostral to AI was a smaller field with a complete tonotopic gradient reversed with respect to that in AI (mirror image representation) and was termed the anterior auditory field (AAF). BFs in the range from 0.1 to 43 kHz, apparently covering the hearing range of the Mongolian gerbil, were found in AI and AAF. Units in these two core fields responded to narrow frequency ranges with short latencies. Ventral to the common high-frequency border to AAF and AI, a rapid transition to very low BFs suggested the presence of a ventral field (V). Caudal to AI two small tonotopically organized fields were identified, a dorsoposterior field (DP) and a ventroposterior field (VP). The VP showed a tonotopic organization mirror imaged to that of AI, i.e. low frequencies were represented rostrally near the caudal border of AI, and high frequencies caudally. The DP showed a concentric frequency organization with high BFs located in the centre. Units in DP and VP fired less strongly, with considerably longer latencies, and responded to a broader range of frequencies than units in AI and AAF. Dorsocaudal to AI a dorsal field (D) was identified, harbouring units that responded to very broad ranges of frequencies. A tonotopic organization of field D could not be discerned. In the border region of AI and D, low-frequency responses were similar to those found in parts of AI and AAF, but without a clear-cut tonotopic organization. This region was termed Ald. The two core fields AI and AAF appeared to be located within the koniocortex, while the remaining fields lay outside. Our data show that the organization of the gerbil auditory cortex is highly elaborate, with parcellation into fields as complex as in cat or primates.

Acoustic Stimulation↗
PubMed1993

Functional organization of auditory cortex in the mongolian gerbil (Meriones unguiculatus). II. Tonotopic 2-deoxyglucose.

The tonotopic organization of the auditory cortex in the Mongolian gerbil was mapped with 2-deoxyfluoro-D-glucose (2DG) using narrow-band frequency-modulated tones of different centre frequency (FM tones) and tones periodically alternating between two different frequencies (alternating tones) as stimuli. Continuous tone bursts of a constant frequency and repetition rate were used in initial experiments. Continuous tones produced 2DG patterns similar to those observed in animals that were not specifically stimulated. With tone bursts of constant frequency and repetition rate variable patterns were observed, some of which could be interpreted only in retrospect in the light of results obtained with FM tones and alternating tones. These stimuli, in contrast, produced differential metabolic responses which in conjunction with 2DG data from monaural animals and electrophysiological data made it possible to distinguish a primary auditory field AI with its dorsal region Ald, an anterior auditory field AAF, a ventral field V, a dorsoposterior field DP and a ventroposterior field VP, a dorsal field D, and in addition an anteroventral field AV. In the largest field (AI) and the smaller rostrally adjacent field AAF, frequency-specific dorsoventral bands of labelling (isofrequency contours) were mapped quantitatively. Bands shifted as a function of frequency relative to each other and to an independent spatial reference line in the lateral hippocampus. Spatial analysis of the single bands obtained with FM tones, and of the double bands obtained with alternating tones in both fields, revealed roughly mirror-imaged tonotopic maps of AI and AAF. In AI the progression from low to high frequencies was from caudal to rostral and in AAF the gradient was reversed, leading to a common high-frequency border of the two fields. In AI, the spatial resolution for frequencies below 16 kHz was in similar intervals per octave and higher for frequencies below 1 kHz. AI showed a somewhat higher spatial resolution for frequencies (at least below 1 kHz) as well as longer isofrequency contours than AAF. The 2-deoxyglucose patterns provided average tonotopic maps and topological data on various fields, as well as reliable landmarks in the gerbil's auditory cortex.

Acoustic Stimulation↗
PubMed1992

Spatial representation of frequency-modulated signals in the tonotopically organized auditory cortex analogue of the chick.

For auditory communication, many birds, including domestic chicks, use a variety of frequency-modulated (FM) sounds. As a first approach to the spatial representation of such sounds in the central auditory system, we have analyzed 2-deoxyglucose (2DG) patterns that were produced by FM stimuli in the tonotopic map of the auditory forebrain area (field L/hyperstriatum ventrale complex) of domestic chicks. Linear FM signals, varying in the depth and range of modulation, and in the direction and rate of the frequency change, were tested. Also included were signals designed to mimic species-specific FM calls. All FM stimuli activated those regions of the map in which frequencies contained in the stimulus spectra were tonotopically represented. However, frequency and amplitude of the FM spectra were not faithfully reproduced by activation of the complete corresponding tonotopic space. FM signals that differed only in the direction of modulation, and therefore had identical long-term spectra, induced maximum 2DG activation at different locations of the tonotopic gradient. FM signals that differed in the rate of change of frequency produced maxima of 2DG uptake at different positions along an isofrequency dimension of the map. These results suggest that the direction of modulation may be represented in a complex fashion along the tonotopic axis of the structure, whereas the rate of change of frequency may be represented along an isofrequency dimension. None of the experiments provided evidence of FM-selective regions within the auditory forebrain complex. However, numerous telencephalic areas, in addition to the primary auditory area, were strongly activated in chicks stimulated with artificial "species-specific" FM signals. These areas could be involved in the processing of biologically relevant stimuli, requiring attention, recognition, and interpretation of the signals.

Acoustic Stimulation↗
PubMed1992

Processing of frequency-modulated stimuli in the chick auditory cortex analogue: evidence for topographic representations and possible mechanisms of rate and directional sensitivity.

Responses of units in the auditory forebrain (field L/hyperstriatum ventrale-complex) of awake domestic chicks were studied to frequency-modulated (FM) signals and isointensity tone bursts, presented to the ear contralateral to the recording sites. FM signals, linear frequency sweeps in the range of 50 Hz to 10.25 kHz, differed in the rate of change of frequency (RCF) and in the direction of modulation. The majority of RCF response functions obtained could be classified as predominantly ascending and bell shaped. Best rates of change of frequency (BRCFs), assigned to these functions, covered a range of nearly 3 orders of magnitude. BRCFs of the same units for upward (positive BRCFs) and for downward modulations (negative BRCFs) were correlated. The lowest BRCF encountered among all units for a given isointensity ON-response bandwidth (delta FON) increased as a function of delta FON. delta FON was derived from the responses to tone bursts of various frequencies at 70 dB SPL. As delta FON tended to increase with the best frequency (BF) of units the lowest BRCF encountered among all units for a given BF also increased as a function of BF. Positive and negative BRCFs of a unit were also correlated with the slopes of onset latency-frequency relationships below and above BF, respectively. FM responses were optimal, when the frequency-specific latency differences at a given unit were compensated by the direction and rate of frequency change in the signal. FM-directional sensitivity varied with BF. Most units with BFs below about 2 kHz preferred upward modulations, while those with BFs above 2 kHz preferred downward modulations. Directional preference and sensitivity correlated with asymmetric distributions of inhibitory sidebands around BF, as derived from the analysis of OFF-responses.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed1992

Postnatal shift of tonotopic organization in the chick auditory cortex analogue.

The existence of an ontogenetic shift of tonotopic organization throughout the auditory pathway concomitant with cochlea maturation is a matter of controversy. Using the 2-deoxyglucose method we demonstrate here for the first time the shift phenomenon in an auditory forebrain structure, field L, the auditory cortex analogue of the chick. During the first postnatal month isofrequency contours move to positions where, in younger chicks, lower frequencies (up to half an octave) are represented. This developmentally changing place code of sound frequencies at the forebrain level is similar to the one previously reported for brain stem auditory nuclei. It raises the question of constancy of frequency-related pitch perception during development and may be a complication of early auditory learning and memory.

Acoustic Stimulation↗
PubMed1991

Parvalbumin-, calretinin- and calbindin-D28k-immunoreactivity and GABA in a forebrain region involved in auditory filial imprinting.

The distribution and morphology of neurons containing the Ca-binding proteins parvalbumin (PV), calbindin-D28k (CaBP) and calretinin (CaR) are described in a rostral forebrain region (MNH) of the chick, known to be involved in auditory filial imprinting. PV immunoreactivity is chiefly a marker for numerous large to medium-sized neurons in the neostriatal part of MNH. They show patchy staining of their dendrites, but PV-positive spines are not visible. CaBP is represented in a different neuron population with on the average slightly smaller-sized somata, which carry long, spiny, CaBP-positive dendrites. In contrast to PV and CaBP, CaR immunoreactivity is a marker chiefly for neuropil in MNH but only for few stained neurons. They may be spiny and show the largest size variations. The density of CaR-immunoreactive neuropil is highest in the hyperstriatal part of MNH. Double immunostaining for PV and CaBP reveals that these proteins are expressed mostly in different neuron populations, with only few neurons containing both proteins. These neuron populations appear to form an interconnected network within MNH. A possible relationship between the expression of either Ca-binding protein and the presence of the inhibitory transmitter GABA is also examined. The GABA-antibody labels scattered, very small to medium-sized neurons and dense punctate neuropil. The comparison of the area histograms of somata reveals an overlap with all 3 Ca-binding protein containing cell populations, except for a large proportion of small GABA-positive neurons. The characteristics of immunostained neuron populations are compared to the previously described 3 Golgi-types of neurons in MNH, and possibilities of a functional implication of the proteins in MNH plasticity are examined.

Acoustic Stimulation↗
PubMed1991

Functional organization of the avian auditory cortex analogue. I. Topographic representation of isointensity bandwidth.

Bandwidth of auditory units in the chick forebrain (field L/Hv complex) was measured with isointensity tone stimuli. Isointensity bandwidth is topographically represented within the four-layered tonotopically organized structure. It declines continuously from rostrodorsal to caudoventral along the longitudinal axis of two-dimensional best frequency planes (frequency band laminae). Layer-specific differences along the radial axis are also obvious. In the input layer of field L and in Hv ON-response bandwidths are relatively broad. The narrower bandwidths of units in the two postsynaptic layers of field L are probably caused by lateral inhibition mechanisms, as derived from the different topographic representations of OFF-versus ON-response bandwidths. A quantitative comparison of the topographic representation of bandwidth is made with the geometry of the tonotopic organization of the chick auditory forebrain complex, as revealed by 2-deoxyglucose data in a former study. A number of possible input-output transformations are derived from this comparison.

Acoustic Stimulation↗
PubMed1991

Functional organization of the avian auditory cortex analogue. II. Topographic distribution of latency.

Onset latencies of units were measured at 70 dB SPL in the auditory forebrain area (field L/Hv-complex) of awake domestic chicks. Latencies ranged from 8.8 to 75 ms. Latencies of units averaged for octave bands of best frequencies (BF) declined with increasing BF. Latencies were topographically distributed in the radial but not in the longitudinal dimension of frequency band laminae (FB laminae). Latencies were shortest in the input-layer L2 and increased systematically towards the postsynaptic layers L3 and L1/Hv, respectively. This topography visualizes the spatiotemporal spread of onset excitation and reflects the hierarchical processing within the structure. It also indicates a topographical representation of temporal resolution.

Acoustic Stimulation↗
PubMed1991

Functional organization of auditory cortical fields in the Mongolian gerbil (Meriones unguiculatus): binaural 2-deoxyglucose patterns.

Unilaterally deafened (cochlear destruction) gerbils were exposed to white noise after injection of 14-C-2-deoxyglucose. The labelling patterns were compared to those of unstimulated operated animals, noise stimulated control animals and bilaterally ear plugged animals. Serial transverse, horizontal and tangential autoradiographs through the cortex were analysed. In lesioned animals, labelling was strongly reduced on the side contralateral to the lesion in the high frequency regions of A1 and the anterior auditory field (AAF). We assume that these regions correspond to the high frequency EI cell areas. Fine banding could be seen superimposed on this pattern in transverse and tangential sections. We suggest that this may be due to alternating strips of EI and EE cells orthogonal to iso-frequency contours. In the low frequency regions of A1 and AAF, labelling asymmetries were also present, but were less pronounced. We assume that these effects are due to low frequency EE cells. In sub-cortical structures, labelling was reduced in the inferior colliculus and ventral part of the medial geniculate body contralateral to the lesioned ear, but no labelling pattern was visible. We presume that the spatial separation of EE and EI inputs to these structures is not marked enough to allow labelling patterns to be seen. In the superior olivary complex, labelling was reduced on the side contralateral to the lesioned ear in the medial dendritic field of the medial superior olivary nucleus and in the nucleus of the trapezoid body. Ipsilateral to the lesioned ear, labelling was reduced in the lateral dendritic field of the medial superior olive.

Acoustic Stimulation↗
PubMed1991

Parvalbumin and calbindin-D28K immunoreactivity as developmental markers of auditory and vocal motor nuclei of the zebra finch.

The posthatch developmental profiles of parvalbumin and calbindin-D28K immunoreactivity were compared for the auditory nucleus mesencephalicus lateralis pars caudalis in the midbrain, n. ovoidalis in the thalamus, and telencephalic field L, as well as for the telencephalic vocal motor nuclei hyperstriatum ventrale pars caudalis and n. robustus archistriatalis. The two calcium-binding proteins showed specific temporal patterns of expression in each nucleus, without following an ascending or descending sequence. Calbindin-D28K immunoreactivity usually preceded parvalbumin immunoreactivity. Onset of expression, especially of parvalbumin-immunostaining, was earlier in auditory nuclei than in vocal motor nuclei. The developmental order of appearance of immunoreactivity in somata, dendrites and axons was different in various brain regions. In some structures parvalbumin or calbindin-D28K immunoreactivity occurred only transiently. The two antibodies bound to separate but spatially complementary groups of cells in the nucleus mesencephalicus lateralis pars dorsalis and n. ovoidalis, as has previously been described in visual nuclei. This pattern was maintained into adulthood. These hitherto unknown subcompartments may reflect internal functional organization in these nuclei. A transitory neostriatal zone containing parvalbumin-positive neurons and fibres was observed between the immature field L and the emerging hyperstriatum ventrale pars caudalis. Some comparative aspects are discussed as to the way in which neurons distinguished by the two Ca-binding proteins may differ in energy metabolism, activity pattern and other functional mechanisms.

Animals↗
PubMed1991

Auditory cortex: comparative aspects of maps and plasticity.

Much recent work in the field of auditory cortex analysis consists of an intensified search for complex sound representation and sound localization mechanisms using tonotopic maps as a frame of reference. Mammalian species rely on parallel processing in multiple tonotopic and non-tonotopic maps but show different degrees of unit complexity, and orderly representation of acoustic dimensions in such maps depending on the predictability of sounds in their environment. Birds appear to rely chiefly on one tonotopic map which harbours multidimensional complex representations. During development and after partial hearing loss, tonotopic organization changes in a predictable manner. Learning also modifies the spatial representation of sounds and even modifies tonotopic organization, but the spatial rules involved in this process have not yet emerged.

Animals↗