Rat Auditory Cortex Research Articles

Long-term depression induced by local tetanic stimulation in the rat auditory cortex

In sensory cortices, synaptic plasticities such as long-term potentiation (LTP) and long-term depression (LTD) have important roles in the development of neural circuits and sensory information processing. However, the differential roles and mechanisms of the various types of LTP and LTD are not clear. In the present study, we investigated LTP and two types of LTD in slices obtained from the rat auditory cortex. Supragranular field potentials elicited by layer VI stimulation were recorded through a metal electrode. Transsynaptic field potentials exhibited marked LTP after tetanic stimulation (TS, 100 Hz for 1 s) was applied to layer VI. The same field potential components exhibited LTD after low-frequency stimulation (LFS, 1 Hz for 900 s) was applied to layer VI. LTD of supragranular field potentials was also induced by local TS applied to supragranular layers 0.3 mm from the recording site. Neither LTP nor LTD of either type was induced in the presence of 50 μM d-(−)-2-amino-5-phosphonovalerate (APV), an NMDA receptor antagonist. However, 500 μM (+)-α-methyl-4-carboxyphenylglycine (MCPG), an antagonist of metabotropic glutamate receptors, had no effect. LTD induced by LFS and that induced by local TS were suppressed in the presence of 3 μM bicuculline, an antagonist of GABA A receptors. Each of these forms of LTD occluded the other. These results and intracellular recordings in supragranular pyramidal neurons during LFS and local TS strongly suggest that the two types of LTD share common neural circuits for their induction.

Spectral and Temporal Processing in Rat Posterior Auditory Cortex

The rat auditory cortex is divided anatomically into several areas, but little is known about the functional differences in information processing between these areas. To determine the filter properties of rat posterior auditory field (PAF) neurons, we compared neurophysiological responses to simple tones, frequency modulated (FM) sweeps, and amplitude modulated noise and tones with responses of primary auditory cortex (A1) neurons. PAF neurons have excitatory receptive fields that are on average 65% broader than A1 neurons. The broader receptive fields of PAF neurons result in responses to narrow and broadband inputs that are stronger than A1. In contrast to A1, we found little evidence for an orderly topographic gradient in PAF based on frequency. These neurons exhibit latencies that are twice as long as A1. In response to modulated tones and noise, PAF neurons adapt to repeated stimuli at significantly slower rates. Unlike A1, neurons in PAF rarely exhibit facilitation to rapidly repeated sounds. Neurons in PAF do not exhibit strong selectivity for rate or direction of narrowband one octave FM sweeps. These results indicate that PAF, like nonprimary visual fields, processes sensory information on larger spectral and longer temporal scales than primary cortex.

Dynamic topography and receptive fields in a model of auditory cortical plasticity

Self-organizing maps provide a useful framework for exploring the mechanisms of experience-dependent changes in auditory representations, including those induced by learning. Such models do a good job of explaining many of the changes in tonotopic structure and neural sensitivities produced by classical and operant conditioning involving pure tones [1], but are not able to account for several effects seen after cortical microstimulation, or after basal forebrain stimulation is repeatedly paired with presentations of sounds containing multiple frequencies. In particular, electrical stimulation of rat auditory cortex produces more changes in the responses properties of adjacent sites than they do at the site of stimulation [2], and these receptive field changes are not consistent with a process that makes the neighboring neurons more similar to the most strongly activated neurons. We developed a simple mapping network with a center-surround neighborhood function, and a cumulating training function, to assess whether such non-Hebbian learning could account for the kinds changes in cortical response properties seen after neurostimulation. The model exhibits many of the properties of self-organizing maps, but with more dynamic interactions between adjacent nodes that may better account for the variability in auditory cortical plasticity observed experimentally. Ongoing simulations with this model are providing new insights into how complex perceptual experiences restructure existing cortical representations.

Muscarinic M2and M1Receptors Reduce GABA Release by Ca2+Channel Modulation Through Activation of PI3K/Ca2+-Independent and PLC/Ca2+-Dependent PKC

We measured pharmacologically isolated GABAergic currents from layer II/III neurons of the rat auditory cortex using patch-clamp recording. Activation of muscarinic receptors by muscarine (1 microM) or oxotremorine (10 microM) decreased the amplitude of electrically evoked inhibitory postsynaptic currents to about one third of their control value. Neither miniature nor exogenously evoked GABAergic currents were altered by the presence of muscarinic agonists, indicating that the effect was spike-dependent and not mediated postsynaptically. The presence of the N- or P/Q-type Ca(2+) channel blockers omega-conotoxin GVIA (1 microM) or omega-AgaTx TK (200 nM) greatly blocked the muscarinic effect, suggesting that Ca(2+)-channels were target of the muscarinic modulation. The presence of the muscarinic M(2) receptor (M(2)R) antagonists methoctramine (5 muM) or AF-DX 116 (1 microM) blocked most of the muscarinic evoked inhibitory postsynaptic current (eIPSC) reduction, indicating that M(2)Rs were responsible for the effect, whereas the remaining component of the depression displayed M(1)R-like sensitivity. Tissue preincubation with the specific blockers of phosphatidyl-inositol-3-kinase (PI(3)K) wortmannin (200 nM), LY294002 (1 microM), or with the Ca(2+)-dependent PKC inhibitor Gö 6976 (200 nM) greatly impaired the muscarinic decrease of the eIPSC amplitude, whereas the remaining component was sensitive to preincubation in the phospholipase C blocker U73122 (10 microM). We conclude that acetylcholine release enhances the excitability of the auditory cortex by decreasing the release of GABA by inhibiting axonal V-dependent Ca(2+) channels, mostly through activation of presynaptic M(2)Rs/PI(3)K/Ca(2+)-independent PKC pathway and-to a smaller extent-by the activation of M(1)/PLC/Ca(2+)-dependent PKC.

Early music exposure modifies GluR2 protein expression in rat auditory cortex and anterior cingulate cortex

GluR2, a major subunit in AMPA receptor, plays an important role in brain functional activity. We studied the effect of music exposure during development on the expression level of GluR2 proteins in the auditory cortex (AC) and anterior cingulate cortex (ACC) of SD rats. Rats were divided into three groups, Music1 (exposed to Nostalgy) group, Music2 (exposed to Wishmaster) group, and control (no music exposure) group. For music exposure groups, rats were exposed to music from postnatal day (PND) 14, and the expression levels of GluR2 proteins were determined at PND 28, 42 and 56. For the control group, the expression levels of GluR2 proteins were determined at PND1, 3, 5, 7, 9, 11, 14, 21, 28, 42, and 56. Results showed an age-dependent expression of GluR2 proteins in control rats. In AC, exposure to Music2 dramatically increased the expression of GluR2, while exposure to Music1 had no effect. In ACC, we found remarkable discrepancies in time-dependent expression of GluR2 between music exposed rats and control rats. These results indicate that exposure to music can modify the expression level of GluR2 protein in AC and ACC.

Efferent connections of the ventral auditory area in the rat cortex: implications for auditory processing related to emotion

In the rat auditory cortex, ventral (VA) and posterodorsal (PD) areas are the two major auditory fields that receive thalamic afferents from the dorsal division of the medial geniculate body (MGD). VA and PD are presumed to serve distinct functions in tandem as the pair of major cortical recipients of extralemniscal thalamic inputs. To deduce the functional significance of VA, efferent connections of VA were examined with the anterograde tracer biocytin. VA lies primarily in the ventral margin of area Te1 and represents frequencies primarily < 15 kHz [Donishi, T., Kimura, A., Okamoto, K. & Tamai, Y. (2006) Neuroscience, 141, 1553-1567.] Biocytin was iontophoretically injected into cortical regions which were defined as VA based on histological location, auditory response and thalamocortical connectivity. Anterograde labelling revealed two important aspects of cortical projections. First, VA sent a projection to a well-confined region in the caudal end of the insular cortex (Ins) pivotal for fear memory formation during aversive conditioning. Second, VA sent parallel projections to cortical regions that probably comprise the other nonprimary auditory fields, including PD. The results suggest that VA relays auditory input from the MGD to the Ins for affective memory formation and at the same time dispatches the auditory signal, which may represent emotional content, to the remaining nonprimary auditory fields. PD is assumed to play a pivotal role in auditory spatial processing for directed attention (Kimura et al., 2004). As the counterpart of PD, VA is assumed to give rise to another major stream of cortical information processing, most probably related to emotion.

Multiparametric Auditory Receptive Field Organization Across Five Cortical Fields in the Albino Rat

The auditory cortex of the rat is becoming an increasingly popular model system for studies of experience-dependent receptive field plasticity. However, the relative position of various fields within the auditory core and the receptive field organization within each field have yet to be fully described in the normative case. In this study, the macro- and micro-organizational features of the auditory cortex were studied in pentobarbital-anesthetized adult rats with a combination of physiological and anatomical methods. Dense microelectrode mapping procedures were used to identify the relative position of five tonotopically organized fields within the auditory core: primary auditory cortex (AI), the posterior auditory field (PAF), the anterior auditory field (AAF), the ventral auditory field (VAF), and the suprarhinal auditory field (SRAF). AI and AAF both featured short-latency, sharply tuned responses with predominantly monotonic intensity-response functions. SRAF and PAF were both characterized by longer-latency, broadly tuned responses. VAF directly abutted the ventral boundary of AI but was almost exclusively composed of low-threshold nonmonotonic intensity-tuned responses. Dual injection of retrograde tracers into AI and VAF was used to demonstrate that the sources of thalamic input from the medial geniculate body to each area were essentially nonoverlapping. An analysis of receptive field parameters beyond characteristic frequency revealed independent spatially ordered representations for features related to spectral tuning, intensity tuning, and onset response properties in AI, AAF, VAF, and SRAF. These data demonstrate that despite its greatly reduced physical scale, the rat auditory cortex features a surprising degree of organizational complexity and detail.

Anesthesia suppresses nonsynchronous responses to repetitive broadband stimuli

Although many aspects of sensory processing are qualitatively similar in awake and anesthetized subjects, important state-dependent differences are known to exist. To investigate the effects of anesthesia on temporal processing in rat auditory cortex, multi-unit neural responses to trains of broadband clicks were recorded prior to, 15 min following, and 5 h following the administration of a ketamine-based anesthetic. While responses to clicks in isolation were relatively stable between states, responses to subsequent clicks exhibited increases in latency, peak latency, response duration, and post-onset suppression under anesthesia. Ketamine anesthetic reduced the maximum rate at which multi-unit clusters entrained to repeated clicks. No multi-unit clusters entrained to stimulus presentation rates greater than 33 Hz under anesthesia, compared with 85% and 81% in the pre- and post-anesthetic condition, respectively. Anesthesia also induced oscillatory activity that was not present in awake subjects. Finally, ketamine anesthesia abolished all tonic excitatory and suppressive nonsynchronous responses to click trains. The results of this study suggest that ketamine-based anesthesia significantly alters neural coding of broadband click trains in auditory cortex.

Spike Time-Dependent Plasticity Induced by Intra-Cortical Microstimulation in the Auditory Cortex

Intrinsic plastic properties in the auditory cortex can cause dynamic remodeling of the functional organization according to trainings. Neurorehabilitation will therefore potentially benefit from electrical stimulation that can modify synaptic strength as desired. Here we show that the auditory cortex of rats can be modified by intracortical microstimulation (ICMS) associated with tone stimuli on the basis of the spike time-dependent plasticity (STDP). Two kinds of ICMS were applied; a pairing ICMS following a tone-induced excitatory synaptic input and an anti-paring ICMS preceding a tone-induced input. The pairing and anti-pairing ICMS produced potentiation and depression, respectively, in responses to the paired tones with a particular test frequency, and thereby modified the tuning property of the auditory cortical neurons. In addition, we demonstrated that our experimental setup has a potential to directly measure how anesthetic agents and pharmacological manipulation affect ICMS-induced plasticity, and thus will serve as a powerful platform to investigate the neural basis of the plasticity.

Gene expression and plasticity in the rat auditory cortex after bilateral cochlear ablation

Conclusion. The plastic changes in the auditory cortex after bilateral cochlear ablation are related to the immediate early genes as well as the neural plasticity-related genes. In addition, cross-modal plasticity may play an important role in the early changes in the auditory cortex after bilateral cochlear ablation. Objectives. The purpose of this study was to identify candidate genes involved in the normal development of primary auditory cortex during the critical period as well as those genes specifically modulated under conditions of sensory deafferentation by bilateral cochlear ablation. Materials and methods. We produced a bilaterally deaf rat model and used DNA microarray technology to analyze differential gene expression in the primary auditory cortex of bilateral cochlear ablated and sham-operated age-matched control rats. Gene expression in the auditory cortex was compared at 2, 4, and 12 weeks after surgery. For selected genes, the changes in gene expression were confirmed by real-time polymerase chain reaction (PCR). Results. In the cochlear ablation groups, the expression of immediate early genes (Egr1, 2, 3, 4, c-fos, etc.) and neural plasticity-related genes (Arc, Syngr1, Bdnf, etc.) was decreased at 2 weeks and increased at 4 weeks. The expression of neurotransmission-related genes (Gabra5, Chrnb3, Chrne, etc.) was decreased at 12 weeks.

Penetration-Type Microelectrode Array with a Silicone-Rubber Substrate

This paper proposes a penetration-type tungsten microelectrode array on a flexible silicone rubber substrate for neural recording from a desired cortical layer. Our evaluation experiments confirmed that the flexible substrate keeps the penetration depth of each electrode constant and allows simultaneous multipoint recording of spike potentials from a desired neocortical layer. Penetration of the stiff and flexible arrays into agarose, which has the curvature comparable to that of the rat brain, revealed that the electrodes at the edge of the stiff array had up to 150 μm error in its penetration depth, while the penetration depth of the flexible array was approximately constant across the electrodes (ANOVA, p=0.835). Electrophysiological experiments in the rat auditory cortex demonstrated that the simultaneous multipoint recording of the acoustically evoked spike potentials was feasible with the flexible array. A series of penetration trials and characteristic frequency estimations successfully identified the primary auditory cortex by assuring a gradual increase in the characteristic frequencies from caudal to rostral. This result suggests that the proposed electrode is suitable for acute experiments requiring repeated penetration and precision positioning of penetration sites.

Zinc May Play Major Role In Mechanism of Fear

Back to table of contents Previous article Next article Clinical & Research NewsFull AccessZinc May Play Major Role In Mechanism of FearJoan Arehart-TreichelJoan Arehart-TreichelSearch for more papers by this authorPublished Online:17 Nov 2006https://doi.org/10.1176/pn.41.22.0025Although fear is known to arise from the amygdala—that almond-shaped labyrinth located in front of the hippocampus—the molecular mechanisms of fear production have remained elusive.Then, a few months ago, Gleb Shumyatsky, Ph.D., an assistant professor of genetics at Rutgers University; Nobel Prize–winning psychiatrist Eric Kandel, M.D., of Columbia University, and colleagues reported that a protein called stathmin, made in the amygdala, appears to be crucial for both the expression of innate fear and the formation of memory for learned fear (Psychiatric News, February 3).Now more insights into the molecular mechanics of fear production appear to have been obtained by Shumyatsky, Kandel, and their group, and the metal zinc seems to be a crucial player. Results were published in the September 27 online early edition of the Proceedings of the National Academy of Sciences.First the scientists found that zinc is plentiful in sections of the rat amygdala as well as in the rat auditory cortex, which sends auditory information to the amygdala during fear learning. Then they discovered that those nerves in the rat amygdala that use the neurotransmitter glutamate release zinc as well as glutamate when communicating with each other, and that release boosts electrical transmission between the nerves.Thus zinc may well contribute to the learning of fear, the researchers concluded. Or as the lead researcher, Vadim Bolshakov, Ph.D., director of the Cellular Neurobiology Laboratory at McLean Hospital, put it in an accompanying press release: “Our results provide the first direct evidence that zinc released during the communication between neurons has an impact on neurotransmission in the amygdala, thus potentially contributing to fear learning.”The findings may also lead to a new classification of anxiety disorders, Shumyatsky told Psychiatric News. “Our new study, along with our earlier work... demonstrates that the neuroanatomic circuits of fear and fear behaviors have their own molecular substrates. This, in turn, suggests that anxiety disorders are not of one common molecular origin, but instead have their specific molecular signatures..., and perhaps in the future will allow for a new type of classification of anxiety states according not only to their behavioral phenotypes, but also with regard to their anatomic and molecular characteristics.”And the results might even lead to new antianxiety drugs, Shumyatsky speculated. “In our study, a gene encoding [the zinc transporter, which is a specific marker for zinc-containing nerves, was] expressed in the cortico-amygdala pathway, but not in the thalamo-amygdala pathway. These two parallel neural pathways are important in relaying fearful stimulus information... to the amygdala. Which of these two pathways is more important, or whether they are equally important, for fear behavior is not clear yet. However, their differences in zinc requirement suggest [that we might be able to design drugs] to target one type of fear processing versus another.”The study was funded by the National Institutes of Health, the Esther A. and Joseph Klingenstein Fund, the National Alliance for Research on Schizophrenia and Depression, the New Jersey Governor's council on Autism, and the Charles and Johanna Busch Memorial Fund.An abstract of “Synaptically Released Zinc Gates Long-Term Potentiation in Fear Conditioning Pathways” is posted at<www.pnas.org/cgi/content/abstract/0607131103v1>.▪ ISSUES NewArchived

Sound sequence discrimination learning motivated by reward requires dopaminergic D2 receptor activation in the rat auditory cortex

We have previously reported that sound sequence discrimination learning requires cholinergic inputs to the auditory cortex (AC) in rats. In that study, reward was used for motivating discrimination behavior in rats. Therefore, dopaminergic inputs mediating reward signals may have an important role in the learning. We tested the possibility in the present study. Rats were trained to discriminate sequences of two sound components, and licking behavior in response to one of the two sequences was rewarded with water. To identify the dopaminergic inputs responsible for the learning, dopaminergic afferents to the AC were lesioned with local injection of 6-hydroxydopamine (6-OHDA). The injection attenuated sound sequence discrimination learning, while it had no effect on discrimination between the sound components of the sequence stimuli. Local injection of 6-OHDA into the nucleus accumbens attenuated sound discrimination learning. However, not only discrimination learning of sound sequence but also that of the sound components were impaired. SCH23390 (0.2 mg/kg, i.p.), a D1 receptor antagonist, had no effect on sound sequence discrimination learning, while it attenuated the licking behavior to unfamiliar stimuli. Haloperidol (0.5 mg/kg, i.p.), a D2 family antagonist, attenuated sound sequence discrimination learning, while it had no clear suppressive effect on discrimination of two different sound components and licking. These results suggest that D2 family receptors activated by dopaminergic inputs to the AC are required for sound sequence discrimination learning.

Nonmonotonic Synaptic Excitation and Imbalanced Inhibition Underlying Cortical Intensity Tuning

Intensity-tuned neurons, characterized by their nonmonotonic response-level function, may play important roles in the encoding of sound intensity-related information. The synaptic mechanisms underlying intensity tuning remain unclear. Here, in vivo whole-cell recordings in rat auditory cortex revealed that intensity-tuned neurons, mostly clustered in a posterior zone, receive imbalanced tone-evoked excitatory and inhibitory synaptic inputs. Excitatory inputs exhibit nonmonotonic intensity tuning, whereas with tone intensity increments, the temporally delayed inhibitory inputs increase monotonically in strength. In addition, this delay reduces with the increase of intensity, resulting in an enhanced suppression of excitation at high intensities and a significant sharpening of intensity tuning. In contrast, non-intensity-tuned neurons exhibit covaried excitatory and inhibitory inputs, and the relative time interval between them is stable with intensity increments, resulting in monotonic response-level function. Thus, cortical intensity tuning is primarily determined by excitatory inputs and shaped by cortical inhibition through a dynamic control of excitatory and inhibitory timing.

A new planar multielectrode array: recording from a rat auditory cortex

In the study of the spatiotemporal properties of the cortex, a demand often arises for recording local field evoked potentials (LFEP) and neural spikes from a quantity of points at close range from each other. In such a situation a device composed of a lot of electrodes assembled in a single bunch would be suitable. Such circumstances gave us the impetus to create the device described in this paper, namely a new planar electrode array for in vivo multisite extracellular recording. The device is made of plastic and includes platinum electrodes 50 µm in diameter. The array of 64 incorporated microelectrodes is placed on the surface of the cortex of anesthetized rats. Recordings could be made through all electrodes for more than 1 h without damage to the cortex. The inter-polar distance is approximately 100 µm so that each individual electrode can record activity from a separate population of neurons near the cortical surface. The recording system described here is highly useful for visualizing spatiotemporal structure of the cortical activities and for imaging dynamic neuronal assemblies.

Layer-specific short-term dynamics in network activity in the cerebral cortex

Optical imaging with a voltage-sensitive dye was conducted in frontal slices of rat auditory cortex to study spatiotemporal patterns of response to repetitive electrical stimulation. When the rate of repetitive stimulation increased to 40 Hz, the amplitude ratio of the response after the fifth stimulus to the response after the first stimulus was significantly smaller in layers II/III than in layer IV or in layers V/VI. Similar results were obtained regardless of where electrical stimulation was applied. When the rate of stimulation was at 10 Hz, no difference was observed in response ratios among layers. These results show that the manner of responding to repetitive stimulation is different among layers and that it is stimulation rate-dependent.

The effect of early auditory deprivation on the age-dependent expression pattern of NR2B mRNA in rat auditory cortex

NMDA receptors have been well shown to be involved in neuronal plasticity. In order to understand the role of NR2B subtype NMDA receptors in auditory function development, the present study investigated the effect of early auditory deprivation on the expression of NR2B mRNA in rat auditory cortex (AC) during postnatal development. For normal rats, the NR2B mRNA expression was highest at birth (postnatal day 1 [P1]) and declined rapidly to low level during adulthood. However, during the critical period of rat auditory development (two to three weeks after birth), there was a transient NR2B expression peak on postnatal day 21 (P21). For the auditory-deprived rats, the general declining trend of NR2B mRNA expression from birth to adult was similar to that observed in the normal group, whereas the expression level from P15 to P27 was significantly lower than normal and the transient peak on P21 disappeared. In both groups, the distribution pattern of NR2B mRNA-positive neurons was also examined in various layers and dorsal, medial and ventral subdistricts of AC. There is no significant effect on the spatial expression of the NR2B mRNA in the AC between normal and deprived group. Our results indicated that the early auditory deprivation decreased the expression levels of NR2B mRNA in AC during the critical period of rat auditory development, suggesting that NR2B plays an important role in the developmental plasticity of auditory function in rats.

Sodium salicylate reduces inhibitory postsynaptic currents in neurons of rat auditory cortex

Sodium salicylate (SS) is a medicine for anti-inflammation and for chronic pain relief with a side effect of tinnitus. To understand the cellular mechanisms of tinnitus induced by SS in the central auditory system, we examined effects of SS on evoked and miniature inhibitory postsynaptic currents (eIPSCs and mIPSCs) recorded from layer II/III pyramidal neurons of rat auditory cortex in a brain slice preparation with whole-cell patch-clamp techniques. Both eIPSCs and mIPSCs recorded from the auditory cortex could be completely blocked by bicuculline, a selective GABA(A) receptor antagonist. SS did not change the input resistance of neurons but was found to reversibly depress eIPSCs in a concentration-dependent manner. SS reduced eIPSCs to 82.3% of the control level at 0.5 mM ( n = 7) and to 60.9% at 1.4 mM ( n = 12). In addition, SS at 1.4 mM significantly reduced the amplitude of mIPSCs from 24.12 ± 1.44 pA to 19.92 ± 1.31 pA and reduced the frequency of mIPSCs from 1.34 ± 0.23 Hz to 0.89 ± 0.13 Hz ( n = 6). Our results demonstrate that SS attenuates inhibitory postsynaptic currents in the auditory cortex, suggesting that the alteration of inhibitory neural circuits may be one of the cellular mechanisms for tinnitus induced by SS in the central auditory region.

Corrigenda

CORRIGENDACorrigendaPublished Online:01 Feb 2006https://doi.org/10.1152/jn.01105.2005Original articlesThe sound-localization ability of catsEnvironmental Enrichment Increases Paired-Pulse Depression in Rat Auditory CortexTopographic Maps of Visual Spatial Attention in Human Parietal CortexMoreSectionsPDF (223 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations Volume 94, August 2005 Pages 1358–1371: Silver MA, Ress D, and Heeger DJ. “Topographic Maps of Visual Spatial Attention in Human Parietal Cortex” (doi:10.1152/jn.01316.2004; http://jn.physiology.org/cgi/content/full/94/2/1358). In Fig. 4, some labels were misrepresented. Specifically, “lateral” and “medial” should be reversed so that “lateral” appears at left and “medial” appears at right. Corrected Fig. 4 is presented here (with original legend). Volume 94, November 2005 Pages 3590–3600: Percaccio CR, Engineer ND, Pruette AL, Pandya PK, Moucha R, Rathbun DL, and Kilgard MP. “Environmental Enrichment Increases Paired-Pulse Depression in Rat Auditory Cortex” (doi:10.1152/jn.00433.2005; http://jn.physiology.org/cgi/content/full/94/5/3590). In Fig. 7, the y-axes were mislabeled. Specifically, “0,” “−100,” “100,” and “0” should be changed to “100,” “50,” “0,” and “−50,” respectively. Corrected Fig. 7 is presented here (with original legend). Pages 3653–3655: Heffner HE and Heffner RS; Reply by Tollin DJ, Populin LC, Moore JM, Ruhland JL, and Yin TCT. Letter to the Editor: “The Sound-Localization Ability of Cats” (doi: 10.1152/jn.00720.2005; http://jn.physiology.org/cgi/content/full/94/5/3653). During publication, some author affiliations at the end of the Reply were misrepresented. The correct affiliations are presented here: L. C. Populin, Department of Anatomy, University of Wisconsin, Madison, Wisconsin; J. M. Moore, J. L. Ruhland, and T. C. T. Yin, Department of Physiology, University of Wisconsin, Madison, Wisconsin. FIG. 4.Left hemisphere attention-related maps in parietal cortex for all 4 subjects (same format as Fig. 3).Download figureDownload PowerPoint FIG. 7.Grand mean average responses of enriched (solid) and standard (dashed) rats to 2 9-kHz tones separated by 500-, 200-, 100-, and 50-ms intervals. The times during which the enriched and standard potentials are significantly different from each other are indicated with dots (paired 2-tailed t-test P < 0.01). These results indicate that paired-pulse depression increases more rapidly as the interval is decreased during enriched compared with standard housing.Download figureDownload PowerPointThis article has no references to display. Download PDF Previous Back to Top FiguresReferencesRelatedInformation Related ArticlesThe sound-localization ability of cats 01 Nov 2005Journal of NeurophysiologyEnvironmental Enrichment Increases Paired-Pulse Depression in Rat Auditory Cortex 01 Nov 2005Journal of NeurophysiologyTopographic Maps of Visual Spatial Attention in Human Parietal Cortex 01 Aug 2005Journal of Neurophysiology More from this issue > Volume 95Issue 2February 2006Pages 1291-1293 Copyright & PermissionsCopyright © 2006 by the American Physiological Societyhttps://doi.org/10.1152/jn.01105.2005History Published online 1 February 2006 Published in print 1 February 2006 Metrics

Discrimination of Direction in Fast Frequency-Modulated Tones by Rats

Fast frequency modulations (FM) are an essential part of species-specific auditory signals in animals as well as in human speech. Major parameters characterizing non-periodic frequency modulations are the direction of frequency change in the FM sweep (upward/downward) and the sweep speed, i.e., the speed of frequency change. While it is well established that both parameters are represented in the mammalian central auditory pathway, their importance at the perceptual level in animals is unclear. We determined the ability of rats to discriminate between upward and downward modulated FM-tones as a function of sweep speed in a two-alternative-forced-choice-paradigm. Directional discrimination in logarithmic FM-sweeps was reduced with increasing sweep speed between 20 and 1,000 octaves/s following a psychometric function. Average threshold sweep speed for FM directional discrimination was 96 octaves/s. This upper limit of perceptual FM discrimination fits well the upper limit of preferred sweep speeds in auditory neurons and the upper limit of neuronal direction selectivity in the rat auditory cortex and midbrain, as it is found in the literature. Influences of additional stimulus parameters on FM discrimination were determined using an adaptive testing-procedure for efficient threshold estimation based on a maximum likelihood approach. Directional discrimination improved with extended FM sweep range between two and five octaves. Discrimination performance declined with increasing lower frequency boundary of FM sweeps, showing an especially strong deterioration when the boundary was raised from 2 to 4 kHz. This deterioration corresponds to a frequency-dependent decline in direction selectivity of FM-encoding neurons in the rat auditory cortex, as described in the literature. Taken together, by investigating directional discrimination of FM sweeps in the rat we found characteristics at the perceptual level that can be related to several aspects of FM encoding in the central auditory pathway.