Publications using TDT

In uncertain, threatening environments, rapid and flexible behavioral decisions are essential for survival. The ventral CA1 region of the hippocampus encodes threatening contexts and can regulate avoidance-related behaviors. While activity patterns in excitatory neurons of vCA1 have been well characterized, the contributions of specific interneuron subtypes to avoidance decisions in threatening situations remain to be fully elucidated. Here, we show that somatostatin expressing (SST) interneurons in vCA1 are selectively recruited during avoidance behavior and play a causal role in shaping behavioral responses in aversive spaces. We find that vCA1 SST interneurons ramp their activity in anticipation of, and during, avoidance. This contrasted with parvalbumin (PV) and vasoactive intestinal peptide (VIP) interneurons, which are preferentially active during exploratory approach behaviors. Unlike other classes of vCA1 interneurons, SST neuron activity more reliably represented the animal’s intention to avoid rather than its spatial position. Moreover, optogenetic silencing of SST interneurons reduced the efficiency of approach-avoidance decisions. These findings identify vCA1 SST interneurons as key regulators of threat assessment, revealing a cell-type-specific mechanism by which vCA1 microcircuits govern avoidance behaviors. This work provides a new framework for understanding hippocampal control of avoidance behavior and highlights SST-expressing interneurons as key contributors to anxiety-related behaviors.

Using external cues to guide behavior is a core function that enables multiple aspects of cognition and attentional control, and deficits in this process are central to many theories of neuro-psychiatric, degenerative, and developmental disorders. Cue detection relies on the precise coordination of neural circuits, with the mediodorsal thalamus (MD) hypothesized to play a pivotal role in orchestrating the relay of cue-based associative information to the prefrontal cortex. The prefrontal cortex comprises multiple subregions, which are believed to differentially contribute to such associative cue-based behaviors. This regional specificity is likely seeded by projection-defined MD→PFC pathways, although the anatomical organization of these discrete channels and their dynamic roles in cue detection are still being defined. Here, we address this gap by combining anatomical circuit mapping of MD-PFC output pathways with in vivo calcium imaging during a cue-based reward conditioning task in mice. These experiments reveal that MD projections to distinct PFC subregions (prelimbic and anterior cingulate cortex) form topographically defined loops, that are characterized by unique patterns of activity across cue-reward learning. Using fiber photometry to monitor changes in calcium activity in axonal projections from the MD to the PFC, we show that during learning, MD projections to the prelimbic subregion are activated by cue presentation, and the dynamics of this activity remain stable across training days. In contrast, MD projections to the anterior cingulate exhibit a learning-dependent suppression of activity that predicts reward approach behavior in late training. Interestingly, the two pathways exhibit opposing activity patterns when the predictive validity of the cue is diminished by extinction training, suggesting distinct functional roles in detecting violations of learned contingencies. Together, these findings reveal previously unrecognized anatomical and functional distinctions within MD-PFC circuits and demonstrate that parallel thalamocortical pathways differentially support cue detection and behavioral flexibility. This work advances understanding of thalamocortical mechanisms underlying cue detection and may inform circuit-based approaches for treating cognitive dysfunction in psychiatric disorders.

The clinical manifestations of mood and psychotic disorders encompass phasic and transdiagnostic features. The complexity of these symptoms may hamper the development of biomarkers for these diagnostic categories. In the present study, machine learning was employed to cluster their transdiagnostic clinical manifestations as a means of developing state-dependent biomarkers with electroencephalography (EEG). This data-driven clustering classified the items of multiple symptom scales into three symptom domains, which subsequently stratified patients with major depressive, bipolar, and schizophrenia spectrum disorders into distinct symptom state groups. The specific brain activity profiles of each stratum were then characterized by resting-state and auditory steady-state EEG paradigms. The resting-state readings of patients in manic states revealed significantly increased gamma and beta oscillations, whereas 40-Hz and 20-Hz auditory steady-state responses (ASSRs) showed no significant differences. These findings suggest that manic states are associated with heightened high-frequency oscillatory activity, represented by gamma and beta oscillations, without a concomitant increase in sensory-evoked information processing precision. Further investigations of excessive gamma and beta oscillations may facilitate the development of state-dependent biomarkers for the assessment, diagnosis, and treatment of manic state symptomatology in clinical psychiatry.

It is widely accepted that tinnitus arises from maladaptive neuroplasticity in the central auditory system, which compensates for reduced peripheral input; notably, the loss of inner hair cell (IHC) synapses is considered a key underlying factor. IHC synapses can immediately and permanently degenerate after noise exposure, independent of hair cell loss, whereas the cell bodies and central projections of cochlear neurons can survive for months to years, providing an extended therapeutic window for improving afferent input through synapse regeneration. Using NHPN-1010 (a combination of 2,4-disulfophenyl-N-tert-butylnitrone and N-acetylcysteine), we propose a delayed treatment strategy (≥ 4 weeks after trauma) for noise-induced tinnitus (NIT) in rats. NHPN-1010 enhanced gap-prepulse inhibition of acoustic startle responses-indicative of diminished tinnitus-like deficits-coupled with a concomitant upregulation of GABAergic inhibition in the dorsal cochlear nucleus, relative to vehicle alone (saline). Furthermore, NHPN-1010, compared to saline, led to increased wave-I amplitudes of auditory brainstem responses, the effect accompanied by a corresponding rise in the number of presynaptic ribbons in IHCs. Our findings suggest that NHPN-1010 plays a therapeutic role in NIT by promoting cochlear synaptogenesis and normalizing central auditory signaling.

Age-related hearing loss (ARHL) is a prevalent sensory deficit characterized by cochlear hair cell apoptosis, yet the underlying epigenetic mechanisms remain unclear. This study investigated the role of E2F1-mediated 53BP2 lactylation in ARHL pathogenesis using naturally aging C57BL/6J mice and HEI-OC1 cochlear hair cell-like cells. We found that E2F1 was significantly upregulated in aged cochleae, correlating with elevated ABR thresholds, hair cell loss, and apoptotic marker expression. In vitro, E2F1 overexpression promoted HEI-OC1 cell apoptosis by stabilizing p53, while E2F1 knockdown attenuated p53 accumulation and cell death under oxidative stress. Mechanistically, mass spectrometry identified 53BP2 lactylation at lysine 476 (K476), which was enhanced by E2F1. The K476R mutation abolished 53BP2-p53 binding, reduced p53 stability, and inhibited apoptosis. Further, E2F1 transcriptionally upregulated p300, a lactyltransferase that directly mediates 53BP2 K476 lactylation. p300 knockdown reversed E2F1-induced 53BP2 lactylation and p53-dependent apoptosis. These findings reveal a novel E2F1-p300-53BP2 lactylation-p53 signaling axis driving cochlear hair cell apoptosis in ARHL, highlighting potential therapeutic targets for age-related hearing loss.

Auditory areas on the superior temporal plane and lateral convexity are key initial stages of speech processing in the human cortex, representing acoustic and phonetic attributes in a temporally precise manner. More complex representations in auditory-related cortex along the ventral and dorsal processing streams and prefrontal cortex are associated with perception and action. In this study, we used intracranial electroencephalography (iEEG) to clarify where and how activity leading to perceptually driven behavioral events emerges. Participants were patients undergoing iEEG monitoring for medically intractable epilepsy. Stimuli were monosyllabic words, and participants pressed a button in response to a semantic target category. Significant high gamma activity after stimulus onset and immediately prior to motor response defined stimulus- and behavior-related activity patterns, respectively. The stimulus-related pattern was more common than behavior-related throughout the cortical auditory hierarchy as well as sensorimotor cortex. Behavior-related activity was sparsely represented, with the highest prevalence in the prefrontal cortex and a more limited representation in anterior temporal and parieto-occipital cortex. Hemispheric asymmetries included a higher prevalence of stimulus-related activity in the right sensorimotor cortex and a higher prevalence of the behavior-related pattern in the left prefrontal cortex. Faster behavioral responses were associated with greater stimulus-locked high gamma power in non-core auditory, prefrontal, and premotor cortex. Results reveal the cortical distribution of sensory stimulus-driven responses and activity time-locked to behavior and provide insights into neural substrates of speech perception.

Background: In Parkinson's disease, motor network electrophysiology frequently exhibits excessive beta oscillations. The cornerstone of therapeutic efficacy lies in the ability to modulate these pathological oscillations. Transcranial alternating current stimulation (tACS), a non-invasive method that applies oscillating electric fields to modulate ongoing brain activity, offers a promising approach. Objective: The objective of the manuscript is to investigate the dose-dependent effects of tACS on motor network cortical neurons in a Parkinson's disease model. Methods: We recorded neuronal spike activity in the motor cortex in parkinsonian non-human primates during tACS to determine how stimulation-induced electric fields affect spike timing. Results: Strong electric fields entrained neural activity at the stimulation frequency but altered the preferred spiking phase. Conversely, weak fields disrupted beta-band synchronization by modulating spike timing and phase preference. Frequency-matched stimulation significantly enhanced entrainment when aligned with endogenous oscillatory activity. Conclusion: Thus, with appropriately chosen stimulation parameters, tACS exhibits significant potential for controlling and modulating pathological oscillatory patterns that are characteristic of many neurological disorders.

Electromotility in mammalian outer hair cells (OHC) is the mechanism underlying cochlear amplification. It is brought about by the piezoelectric-like property of the membrane protein prestin (Slc26a5) that lies in the OHCs lateral plasma membrane. Prestin connects to an underlying cytoskeletal network of circumferential actin filaments that bridge longitudinal spectrin filaments. This network, in turn, lies between the plasma membrane and a closely apposed ER-like tubular array of subsurface cisternae (SSC). Two previous papers examining spectrin knockouts in embryonic hair cells were confined to analyzing the effects on the apical cuticular plate and overlying stereocilia. In this paper, we examine the effects of conditional knockouts of alpha2 spectrin in postnatal OHCs. We find a significant auditory phenotype likely due to the novel disassociation of prestin's gating charge movement from OHC electromotility. In addition, OHCs show enlargement in their SSC and plasma membrane-SSC space with preserved cuticular plates and overlying stereocilia, the latter contrasts with the findings in embryonic knockouts.

Stimulation of sensory vagal pathways is typically delivered via invasive, cervical vagus nerve stimulation (cVNS) or noninvasive, trans-auricular nerve stimulation (taNS). While both methods are investigated therapeutically, their effects on brain physiology remain poorly understood, hindering mechanistic insights and stimulus optimization. In 6 awake nonhuman primates, we recorded cortical vagal-evoked potentials (VEPs) from subdural electrodes placed in prefrontal, sensorimotor and parietal cortical areas, in response to cVNS or taNS. Across 478 different taNS and cVNS protocols, we varied stimulation side, intensity, frequency, pulse count, and pulse width and assessed independent effects on amplitude and latency of early (EC; 30-100 ms), intermediate (IC; 101-200 ms) and late components (LC; 201-500 ms) of VEPs. Fixed and random effects of stimulation parameters and subjects, respectively, on VEPs were assessed using a linear mixed-effects model. Overall, cVNS elicits more robust VEPs than taNS, with larger EC, IC and LC amplitudes, in both hemispheres. cVNS-elicited ECs and LCs are largest in PFC and PC areas, whereas ICs are largest in SM areas. On the other hand, taNS generally does not elicit area-specific responses. cVNS-elicited ECs have slower latency than ta-NS elicited ECs. Higher stimulation frequencies and intensities and a longer pulse width elicit larger ECs and ICs for cVNS, and to some extent for taNS. Both short and long cVNS trains elicit stronger ECs, and long trains elicit slower ICs. Earlobe stimulation elicits VEPs that partially overlap with those from taNS. In conclusion, cVNS and taNS elicit cortical VEPs in a manner consistent with distinct engagement of ascending vagal pathways, with both similarities and differences in the effects of stimulation parameters on evoked responses.

Alzheimer's disease (AD) is a brain condition with heterogeneity in disease progression due to genetic and environmental variables. There is a critical need to better understand the relationship of AD pathologies and potential modifiable factors like hearing loss. Auditory processing measurements in AD mouse models have been reported, but the results are mixed. Most were conducted using evoked potential recordings measured under anesthesia, unlike typical hearing assessments on aging adult humans. Here, we used operant conditioning and signal detection theory to measure daily pure tone behavioral detection throughout the lifespan of trained mutant and wild-type (WT) control APP/PS1 (on a C57BL/6J background) and 5xFAD (on a C57/SJL background) mice. At the conclusion of operant testing, auditory brainstem response (ABR) measures were taken on the same subjects to determine if evoked potentials provided accurate estimates of perceptual abilities. Behavioral detection worsened significantly across the lifespan in APP/PS1 mice, but there were no differences between mutant and WT mice. For 5xFAD mice, behavioral thresholds generally worsened over the lifespan but with substantial variability, which may be explained by genetic heterogeneity among the background strain. There were no differences between 5xFAD mutant and WT mice. ABR hearing threshold estimates generally matched behavioral findings, with APP/PS1 having significantly worse thresholds than 5xFAD mice but no within-model differences between mutants and WTs. The within-subject differences between behavioral and ABR thresholds ranged from <1 dB to over 40 dB across subjects, suggesting physiological measurements of auditory function are not necessarily reflective of an animal's acoustic perception.

Breast cancer patients often exhibit disrupted diurnal rhythms in circulating glucocorticoids (GCs), such as cortisol. This disruption correlates with reduced quality of life and higher cancer mortality; however, the exact cause of this phenomenon remains unclear. Here, we demonstrate that breast tumor-bearing mice exhibit blunted GC rhythms and a loss of diurnal rhythms in the activity of paraventricular hypothalamic neurons expressing corticotropin-releasing hormone (PVNCRH). This change in neuronal activity is mediated by disinhibition from upstream GABAergic neurons. Using chemogenetics to stimulate PVNCRH neurons at different times of day, we show that stimulation just before the light-to-dark transition restores normal GC rhythms, reduces tumor progression, and increases intra-tumor effector T cells (CD8+). Our findings demonstrate that breast cancer distally regulates neurons in the hypothalamus that control the output of the hypothalamic-pituitary-adrenal (HPA) axis and provide evidence that therapeutic targeting of these neurons could mitigate tumor progression via enhancing anti-tumor immunity.

Salivation supports oral health, taste sensation, swallowing, and digestion, but the brain mechanisms that regulate this process remain largely unknown. Here, we identify a salivatory center in the mouse brain stem that integrates sensory and learned anticipatory signals to control salivation. We show that activating choline acetyltransferase-expressing neurons in the inferior salivatory nucleus (IS) is sufficient to trigger saliva secretion. Using fiber photometry, we monitor real-time IS neural responses to mechanosensory and gustatory stimulation and find tight correlation with salivatory output. We further demonstrate that IS neurons receive input from local brain stem circuits, mediating rapid hardwired responses to taste, as well as direct cortical projections. Notably, gustatory cortex input is required for salivatory responses to predictive sensory cues in a Pavlovian conditioning paradigm. Together, our findings define the circuit underlying taste-evoked and anticipatory salivation and provide a foundation for dissecting this autonomic response in health and disease.

The lateral preoptic area (LPO) is a functionally heterogeneous hypothalamic structure that is increasingly recognised for its role in motivated and drug‐seeking behaviours. Although prior studies have shown that LPO neurons exhibit diverse activity patterns during cocaine self‐administration, the specific contributions of glutamatergic and GABAergic populations to conditioned responses to cocaine remain unclear. In this study, we recorded the activity of LPO glutamatergic ( vglut2 ‐expressing) and GABAergic ( vgat ‐expressing) neuronal subpopulations during cocaine conditioning to identify how these cell types respond to drug‐associated cues in awake, behaving mice. Our results revealed that, after cocaine conditioning, both glutamatergic and GABAergic populations showed reduced activity upon entry into the cocaine‐paired chamber. However, only glutamatergic neurons exhibited increased activity when mice entered the saline‐paired chamber. The magnitude of these activity changes was also correlated with behavioural outcomes: reduced GABAergic activity was associated with greater preference for the cocaine‐paired chamber, whereas stronger glutamatergic responses were associated with greater preference for the saline‐paired chamber. These findings indicate that LPO GABAergic and glutamatergic neurons exhibit distinct, cell type–specific patterns during cocaine‐conditioned place preference. Rather than indicating opposing motivational states, the results highlight that LPO activity relates to conditioned behaviours in a cell type– and context‐dependent manner. By linking activity in glutamatergic and GABAergic neurons with conditioned responses, this work provides initial evidence for how LPO circuits may contribute to drug‐associated learning.

Fast-rate speech can encourage perception of subsequent speech as longer-duration (e.g., longer voice onset time) and vice versa. Bosker, Sjerps, and Reinisch [Sci. Rep. 10(1), 5607 (2020)] suggested that these temporal contrast effects (TCEs) (also known as speaking rate normalization) were immune to selective attention (to one of two simultaneous talkers). However, dichotic presentation of different talkers facilitated perception. Here, trials presented the same talker throughout speaking one sentence diotically, two simultaneous sentences diotically, or those two sentences dichotically before target words. TCE magnitudes were similar across all conditions, which suggests that spatial separation of simultaneous sentences does not shape TCEs.

Background/Objectives: Blast-induced hearing loss (BIHL) is a major concern, particularly for military personnel, and is linked to impaired auditory neuron survival and synaptic plasticity. This study investigates the potential of the TrkB agonist 7,8-dihydroxyflavone (7,8-DHF) to reduce the severity of BIHL and promote recovery in a mouse model. Methods: Eight-week-old male C57BL/6J mice were used. A custom-built, compressed air-driven system utilizing a modified paintball apparatus was employed to deliver controlled unilateral double blasts (~22 psi exposure pressure) to the left ear. The blasts were administered 30 min apart. Immediately following the second blast, mice received either 7,8-DHF (10 mg/kg) or vehicle (10% DMSO) via intraperitoneal injection. Auditory brainstem responses (ABRs) were measured in both ears at baseline (pre-blast) and at several post-exposure time points. Results: The consecutive blast exposure induced a significant elevation in ABR thresholds, indicative of hearing loss, in both the ipsilateral (exposed) and contralateral (unexposed) ears of vehicle-treated mice. Notably, mice treated with 7,8-DHF demonstrated a marked improvement in hearing recovery compared to the vehicle group. Significant reductions in ABR thresholds were observed in the ipsilateral ear at 4 weeks post-blast (p < 0.0001) and in the contralateral ear as early as 1-week post-blast (p = 0.0236). However, the recovery was partial, with ABR thresholds plateauing after 4 weeks. Conclusions: A controlled blast model demonstrates that systemic administration of the TrkB agonist 7,8-DHF exerts a protective effect, partially restoring auditory function after blast injury. This supports the therapeutic potential of targeting the BDNF-TrkB signaling pathway for managing BIHL.

Harmonicity is a property of complex sounds such as vocalizations or music, but it remains unclear how harmonicity is processed in the auditory cortex (ACtx). Subregions of ACtx are thought to process harmonic stimuli differently. Selective responses to sound features in ACtx emerge hierarchically from primary ACtx (A1) L4 and secondary ACtx (A2) layer (L)2/3, which is believed to be the most responsive to harmonic sounds. Since harmonic stacks can range from 2 to >10 components, being more similar to naturalistic vocalizations, harmonic sensitivity might also arise hierarchically across layers and areas. We studied responses to harmonic stacks of 2–10 frequencies across A1 L4, A1 L2/3, and A2 L2/3 in adult male and female mice using in vivo two-photon microscopy. We found harmonic-sensitive neurons (HNs) responding only to harmonic stacks but not to individual frequencies in all areas at similar proportions. HNs showed highly nonlinear spectral integration of harmonic frequencies that decreased as the harmonic stacks became more complex. Specifically, onset-biased HNs showed greater nonlinearity than offset-biased HNs only in A1 L4. Moreover, HNs in A1 L4 exhibited higher signal correlation than A2 L2/3. Sound-responsive neurons in A1 L4 have the weakest noise correlation compared with A1 L2/3 and A2 L2/3. Together, harmonic sensitivity is not a unique feature of A2 L2/3 but is already established in A1 L4, where neurons robustly encode harmonic sounds through sparse connections.

Habituation is a crucial sensory filtering mechanism whose dysregulation can lead to a continuously intense world in disorders with hypersensitivity. Although habituation is often termed the simplest form of learning, its circuit mechanisms remain elusive. Conventional peripheral explanations fail to fully account for long-term habituation in complex sensory environments, leading to theories proposing top-down regulation. Here we evaluated two competing top-down mechanistic explanations for habituation in mice (growth in predictive filtering and waning of novelty-driven amplification) and identified an unexpected role for the orbitofrontal cortex (OFC) in predictive filtering. After daily sound exposure, neural habituation in the primary auditory cortex (A1) was reversed by inactivating the OFC. Top-down projections from the OFC, but not other frontal areas, carried predictive signals that grew with daily sound experience and suppressed A1 via somatostatin-expressing inhibitory neurons. Thus, prediction signals from the OFC cancel out anticipated stimuli by generating their 'negative images' in sensory cortices.

Prairie voles ( Microtus ochrogaster ) are a semi-fossorial rodent that are an emerging model in social neuroscience. Comparing laboratory-reared and wild-caught individuals is essential for understanding how environmental history shapes neural and sensory traits and for assessing the ecological validity of laboratory findings. Despite this, relatively few studies have taken this approach. We used auditory brainstem responses (ABRs) to compare ABR thresholds and ABR wave characteristics between laboratory-reared and wild-caught prairie voles. ABR recordings show that, similar to other semi-fossorial rodents, M. ochrogaster exhibit a hearing range of 1–46 kHz with peak sensitivity between 8–24 kHz in wild-caught and 8–32 kHz in laboratory-reared voles. However, wild-caught prairie voles displayed significantly lower ABR thresholds at 1, 4, 8, 16, and 24 kHz compared to laboratory-reared prairie voles. There were significant differences in interpeak latency between both tested groups, with laboratory-reared prairie voles showing faster interpeak latency responses than wild-caught voles. However, there were no differences in amplitude ratios between groups. Laboratory-reared prairie voles showed faster normalized latencies and higher relative amplitude of the binaural interaction component (BIC) of the ABR than wild-caught voles. There were no significant differences in ABR thresholds, interpeak latency, amplitude ratio, normalized latency, and relative amplitude between the sexes. These differences in auditory processing support the importance of integrating both wild and captive populations to advance comparative auditory research.

Introduction Cisplatin-induced ototoxicity remains a major clinical challenge in chemotherapy, with limited pharmacological strategies available to prevent auditory damage. In this study, we explored the protective potential of baicalin, a flavonoid compound, against cisplatin-triggered cochlear injury. Methods In vivo, baicalin was administered to C57BL/6 mice prior to cisplatin treatment. Auditory function was assessed using auditory brainstem response (ABR) and distortion product otoacoustic emission measurements, and cochlear hair cell integrity was examined. In vitro, both House Ear Institute-Organ of Corti 1 (HEI-OC1) auditory cells and cochlear explants were used. Cell viability, apoptosis, mitochondrial reactive oxygen species (ROS) accumulation, and mitochondrial membrane potential (ΔΨm) were evaluated using MitoSOX Red, TMRM, and JC-1 fluorescence probes. The involvement of the p38 MAPK pathway was investigated using anisomycin (an activator) and SB203580 (an inhibitor) at the protein level. Results In vivo, baicalin administration significantly mitigated cisplatin-induced hearing loss, as evidenced by improved ABR and distortion product otoacoustic emission thresholds and preserved cochlear outer hair cell structural and functional integrity. In vitro, baicalin pretreatment significantly improved cell viability and attenuated cisplatin-induced apoptosis. Mechanistically, baicalin markedly reduced mitochondrial ROS accumulation and maintained ΔΨm. Furthermore, baicalin pretreatment effectively inhibited p38 MAPK activation; this protective effect was reversed by anisomycin and mimicked by SB203580. Discussion Collectively, these findings demonstrate that baicalin provides robust otoprotection against cisplatin-induced hearing loss. In vitro studies further indicate that this protective effect is associated with the attenuation of oxidative stress, maintenance of mitochondrial integrity, and inhibition of p38 MAPK–mediated apoptosis. Together, the results highlight baicalin as a promising candidate for therapeutic intervention against cisplatin-induced hearing loss.

Introduction Spectral information of speech sounds is spatially arranged from low to high frequencies in the auditory cortex, known as tonotopic maps. Recently, we identified an envelope steepness map encoding the rise-ramp steepness of sounds, which is located orthogonally to the tonotopic map. Temporal components, particularly the sound envelope defined by the rise-ramp steepness, play a crucial role in speech perception. We hypothesized that the ability to sense temporal components of sounds, such as envelope steepness, would be diminished in aged mice. Methods Responses to variations in rise-ramp time were investigated using transcranial macroscale calcium imaging of the auditory cortices of GCaMP6f-expressing mice. Normalized distance relative to the rise-ramp time of 0.01 ms was plotted for each rise-ramp time (0.1, 1, 10, and 100 ms) in the logarithmic scale graph: the steeper the slope of the fitted regression lines, the greater the distance between the peaks of the rise-ramp time of 0.01 ms and 100 ms. The slope of this regression line was compared between the different age groups: 1/3 months and 6/9/12 months after birth. Results The slope of the fitted regression line for 5 kHz in the bilateral anterior auditory field and 20 kHz in the bilateral primary auditory field was significantly less steep in mice at 6/9/12 months after birth than at 1/3 months after birth. Conclusion The shorter distance from the peak of 0.01 ms to 100 ms in animals 6/9/12 months after birth suggests difficulty in the separation of the rise-ramp time in aged animals. These findings may support the cortical mechanisms underlying age-related decline in speech perception.