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PubMed1988

Role of auditory cortex in the acquisition of differential heart rate conditioning.

Previous findings from our laboratory indicate that lesions of the auditory cortex disrupt the retention of differentially conditioned bradycardiac responses to tonal stimuli in rabbits. In the present experiment, the effect of lesions of the auditory cortex on the acquisition of differential bradycardiac conditioning was examined. The effect of lesions in the auditory cortex were compared to the effect produced by control lesions in the visual cortex. After 7 days of recovery, animals received 7 days of differential Pavlovian bradycardiac conditioning in which one tone (CS+) was paired with the unconditioned stimulus, and another tone (CS-) was never paired with the unconditioned stimulus. All animals demonstrated differential conditioning during the first 3 days of conditioning. On days 4-7, however, auditory cortex lesioned animals did not exhibit significant differential heart rate (HR) conditioning, whereas control animals with lesions in the visual cortex showed no loss of conditioning during this period. The loss of differential conditioning in animals with lesions in the auditory cortex appears to be due to an increase in the magnitude of the response to the CS-. These data support the hypothesis that the auditory cortex serves to inhibit the response to the CS- in differential conditioning of bradycardia to acoustic stimuli, and that the inhibition may be mediated by a descending corticothalamic or corticolimbic pathway.

Animals↗

PubMed1989

Nonlinguistic auditory capabilities in aphasia.

Nonlinguistic auditory capabilities were assessed through psychophysical tests in 11 left-CVA aphasic, four right-CVA nonaphasic, and eight normal male subjects selected from the same age group. The tests included frequency discrimination, gap detection, gap discrimination, frequency sweep discrimination, assessment of the magnitude of the frequency uncertainty effect in the detectability of tones in noise, and assessment of frequency selectivity through simultaneous masked thresholds. Results of these tests were compared to measures of auditory comprehension obtained from the Boston Diagnostic Aphasia Examination, the Porch Index of Communicative Ability, and the Token Test. Nonlinguistic auditory performance of the three subject groups differed significantly from each other. For the left-CVA subjects, frequency sweep discrimination, frequency discrimination, and the frequency uncertainty effect in tone-in-noise detection were the best predictors of verbal auditory comprehension. The right-CVA subjects displayed marked deficits with regard to all pitch-related tests. The findings stress the importance of considering the presence of nonlinguistic auditory dysfunctions when evaluating linguistic auditory capabilities in aphasia.

Adult↗

PubMed1994

Intensity dependence of auditory evoked dipole source activity.

The spatio-temporal approach of dipole source analysis represents a crucial methodological progress in research on individual differences in the dependence of auditory evoked potential amplitude on stimulus intensity (augmenting/reducing) because overlapping subcomponents of the N1/P2-component can be separated and can be related to their generating cortical structures. Basic aspects of the intensity dependence of auditory evoked dipole source activity were analysed in 40 healthy subjects. The evoked responses to binaural 1000-Hz tones at five levels of intensity (60, 70, 80, 90, 100 dB sound pressure level) were recorded at 33 sites across the scalp. The dipole source analysis of the grand average data confirms the reports in the literature that the N1/P2 potentials at the scalp can be explained by two dipoles per hemisphere: a tangential dipole, representing activity of the superior temporal cortex (including primary auditory cortex), and a radial dipole, representing activity of the lateral temporal cortex (secondary auditory areas). The intensity dependence of the tangential dipole activity was significantly more pronounced than that of the radial dipoles, supporting the assumption that radial and tangential dipoles represent different physiological processes. A high reliability of the intensity dependence of the tangential dipole (Pearson correlation: r = 0.88) was found when retesting the subjects after three weeks. Age was negatively correlated with the intensity dependence of the tangential dipole. Dipole source analysis proved to be a reliable method which allows, at least in part, to study separately the intensity dependence of the evoked responses from primary and secondary auditory cortices. This is of importance with regard to the hypothesis that the central serotonergic system modulates the intensity dependence of the evoked N1/P2-response of primary auditory cortex.

Adult↗

PubMed1983

The auditory brainstem nuclei and some of their projections to the inferior colliculus in the North American opossum.

Afferent projections to the inferior colliculus in the North American opossum have been examined using the retrograde transport of horseradish peroxidase. Projections to primarily the contralateral inferior colliculus arise in the dorsal and ventral cochlear nuclei, the auditory nerve nucleus and the spinal trigeminal nucleus pars caudalis, while ipsilateral projections arise in the superior paraolivary nucleus, the ventral nucleus of the trapezoid body, the ventral nucleus of the lateral lemniscus, the paralemniscal nucleus, the deep layer of the superior colliculus and the parabrachial nucleus. Bilateral projections to the inferior colliculus originate within the dorsal column nuclei, the nucleus reticularis gigantocellularis pars ventralis, the lateral and medial superior olivary nuclei, the dorsal nucleus of the lateral lemniscus and the auditory cortex. Nissl, fiber and Golgi-stained preparations were used to study the neuronal organization of those auditory nuclei with projections to the inferior colliculus. Anterograde axonal degeneration and transport techniques revealed that the inferior colliculus is innervated differentially by the dorsal and ventral cochlear nucleus, the superior olivary complex and the auditory neocortex. Axons from the contralateral dorsal cochlear nucleus and the ipsilateral superior olivary complex innervate both the central nucleus and external cortex, whereas those from ventral cochlear nucleus and contralateral, superior olivary complex project to only the central nucleus. Projections from auditory cortex form the complement of those from the cochlear nuclei and superior olivary complex, that is, they terminate in a thin band overlying the dorsal cortex and the superficial layer of external cortex. Our results have been compared with those obtained from eutherian mammals and it is clear that there are striking similarities in neuronal organization and connectivity. Since the opossum is born 12 days after conception and has an extended development in an external pouch, it may be suited for developmental studies of the mammalian auditory connections and the behaviors dependent of them.

Aging↗

PubMed1987

Pentobarbital and ketamine alter the pattern of 2-deoxyglucose uptake in the central auditory system of the gerbil.

Relative 2-deoxyglucose (2-DG) uptake was investigated during pentobarbital and/or ketamine anesthesia, when animals were either kept in silence or stimulated with wide band noise at 85 dB SPL. In the absence of anesthesia, noise stimulation produced a large increase in relative 2-DG uptake, when compared to silence, in all auditory nuclei up to and including the inferior colliculus. Much more modest noise-induced increases were seen in the medial geniculate nucleus and auditory cortex. These effects were markedly altered by anesthesia. Pentobarbital, and especially pentobarbital plus ketamine, enhanced stimulus-evoked increases in relative 2-DG uptake in lower auditory nuclei: the cochlear nuclei, superior olivary complex and ventral nucleus of the lateral lemniscus. At the same time, stimulus-evoked increases were decreased in the dorsal nucleus of the lateral lemniscus and inferior colliculus, and virtually eliminated in the medial geniculate and auditory cortex. The results of this study permit more meaningful comparison of 2-DG techniques with electrophysiological measures of central auditory activity, and illuminate the utility and limitations of each method. The data indicate that 2-DG observations from barbiturate-anesthetized preparations should be interpreted with some caution. They further suggest that the 2-DG technique is inappropriate for the study of stimulus-evoked activity in the medial geniculate and auditory cortex of barbiturate-anesthetized animals.

Acoustic Stimulation↗

PubMed1987

Effect of noise on auditory evoked responses in awake guinea pigs.

Changes in the auditory nerve action potential (AP), evoked responses from the inferior colliculus (IC-ER) and auditory cortex (AC-ER) were assessed after exposure to white noise of 120 dB SPL for 1 h in awake guinea pigs. Auditory thresholds were estimated with the aid of averaged AP, IC-ER and AC-ER, besides the threshold shifts also the changes in amplitude-intensity functions were evaluated. Auditory thresholds for tone pips and clicks increased by 20-30 dB 1 h after exposure and were similar in all the three investigated structures. The maximum threshold shifts for tone pips were observed at 8 kHz and were 33.2 +/- 12.9 dB for AP, 30.4 +/- 12.7 dB for IC-ER and 30.8 +/- 13.0 dB for AC-ER (n = 20). The thresholds recovered to preexposure levels within one week. Reduction in AP and IC-ER amplitudes 1 h after exposure was similar, the amplitude-intensity functions were shifted by 20-40 dB. In contrast, the amplitude-intensity functions in the auditory cortex 1 h after exposure were steeper than before exposure and this amplitude enhancement was present for 24 h after exposure. The enhancement of the AC-ER which resembles recruitment and which may be a sign of hypersensitivity of the animal to auditory stimuli was present only when the animals exposed to noise were awake. The noise exposure in animals anaesthetized with urethane reduced the amplitude-intensity functions of all three recorded potentials.

Anesthesia↗

PubMed1991

Morphology of corticothalamic terminals arising from the auditory cortex of the rat: a Phaseolus vulgaris-leucoagglutinin (PHA-L) tracing study.

Phaseolus vulgaris-leucoagglutinin (PHA-L) injection in the auditory cortex of the rat labeled anterogradely corticothalamic axons whose trajectory, morphology of terminals and their distribution were analyzed in light microscopy. From the primary auditory cortex, corticofugal axons ran in a rostral direction in the white matter (external capsule), and reached the internal capsule by crossing the caudate putamen. Then, they turned caudally, crossed the reticular nucleus (RE) of the thalamus, where some of them were seen to give off collaterals, ramifying in the 'auditory sector' of RE. From RE, the parent corticofugal axons continued in a caudal and medial direction to enter in the medial geniculate body (MGB). Corticofugal axons from the auditory cortex gave rise to 2 distinct types of terminals in the thalamus. First, small boutons (about 1 micron in diameter) were observed in the ventral division of the MGB (v-MGB; the main auditory relay nucleus in the thalamus), in RE, in the lateral part of the posterior thalamic nucleus, in the dorsal division of the MGB (d-MGB), as well as occasionally in the medial division of the MGB. Giant terminals (5-10 microns in diameter) formed the second type of cortical terminals, only present in a restricted zone of the ventral portion of d-MGB. Both types of terminals were observed as boutons 'terminaux' and 'en passant'. The zone of termination in v-MGB and RE varied as a function of the site of cortical injection. The similarity in the morphology and distribution of the terminals of corticothalamic axons arising from the primary auditory cortex with those of the primary somatosensory cortex of the mouse is striking and points to the existence of a basic pattern of connectivity used in corticothalamic processing of sensory information in rodents.

Animals↗

PubMed2005

Left hemisphere specialization for rapid temporal processing: a study with auditory 40 Hz steady-state responses.

OBJECTIVE: To investigate rapid temporal processing in the auditory cortex by using auditory 40 Hz steady-state responses (SSRs). METHODS: A 40 Hz tone-burst at 500 Hz spectral frequency was presented monaurally to record SSRs in 10 normal subjects. The recording electrodes were placed over C1, C2, C3, C4, C5, C6, T3, T4, Fz, Cz and Pz, referring to an electrode at the 7th cervical spinous process. For comparison, unstimulated SSRs were recorded. A total of 200 responses of 1s epoch were averaged and subjected to discrete fast Fourier transforms to yield the amplitude and phase of the 40 Hz component. The coherence (Coh) values of the 40 Hz component between homologous electrodes were also calculated. RESULTS: At the temporal electrodes contralateral to the stimulated ear, the amplitude was significantly larger and its phase was significantly smaller than those of the ipsilateral side. The interhemispheric Coh between T3 and T4 in response to right ear stimulation was significantly greater than those of left ear stimulation or the unstimulated condition. CONCLUSIONS: Our results suggest that 40 Hz auditory information is predominantly processed in the left auditory cortex, interacting with the right hemisphere. This finding is consistent with the fact that the left auditory cortex plays an important role in rapid temporal processing. SIGNIFICANCE: Auditory 40 Hz SSRs with Coh analysis are useful for investigating the left hemisphere specialization for rapid temporal processing.

Acoustic Stimulation↗

PubMed2005

Electrophysiological and speech perception measures of auditory processing in experienced adult cochlear implant users.

OBJECTIVE: This study determined the relationship between auditory evoked potential measures and speech perception in experienced adult cochlear implant (CI) users and compared the CI evoked potential results to those of a group of age- and sex-matched control subjects. METHODS: CI subjects all used the Nucleus CI-22 implant. Middle latency response (MLR), obligatory cortical potentials (CAEP), mismatch negativity (MMN) and P3a auditory evoked potentials were recorded. Speech perception was evaluated using word and sentence tests. RESULTS: Duration of deafness correlated with speech scores with poor scores reflecting greater years of deafness. Na amplitude correlated negatively with duration of deafness, with small amplitudes reflecting greater duration of deafness. Overall, N1 amplitude was smaller in CI than control subjects. Earlier P2 latencies were associated with shorter durations of deafness and higher speech scores. In general, MMN was absent or degraded in CI subjects with poor speech scores. CONCLUSIONS: Auditory evoked potentials are related to speech perception ability and provide objective evidence of central auditory processing differences across experienced CI users. SIGNIFICANCE: Since auditory evoked potentials relate to CI performance, they may be a useful tool for objectively evaluating the efficacy of speech processing strategies and/or auditory training approaches in both adults and children with cochlear implants.

Acoustic Stimulation↗

PubMed2004

PET imaging of the 40 Hz auditory steady state response.

The auditory steady state response (aSSR) is an oscillatory electrical potential recorded from the scalp induced by amplitude-modulated (AM) or click/tone burst stimuli. Its clinical utility has been limited by uncertainty regarding the specific areas of the brain involved in its generation. To identify the generators of the aSSR, 15O-water PET imaging was used to locate the regions of the brain activated by a steady 1 kHz pure tone, the same tone amplitude modulated (AM) at 40 Hz and the specific regions of the brain responsive to the AM component of the stimulus relative to the continuous tone. The continuous tone produced four clusters of activation. The boundaries of these activated clusters extended to include regions in left primary auditory cortex, right non-primary auditory cortex, left thalamus, and left cingulate. The AM tone produced three clusters of activation. The boundaries of these activated clusters extended to include primary auditory cortex bilaterally, left medial geniculate and right middle frontal gyrus. Two regions were specifically responsive to the AM component of the stimulus. These activated clusters extended to include the right anterior cingulate near frontal cortex and right auditory cortex. We conclude that cortical sites, including areas outside primary auditory cortex, are involved in generating the aSSR. There was an unexpected difference between morning and afternoon session scans that may reflect a pre- versus post-prandial state. These results support the hypothesis that a distributed resonating circuit mediates the generation of the aSSR.

Adult↗

PubMed2004

ARTSTREAM: a neural network model of auditory scene analysis and source segregation.

Multiple sound sources often contain harmonics that overlap and may be degraded by environmental noise. The auditory system is capable of teasing apart these sources into distinct mental objects, or streams. Such an 'auditory scene analysis' enables the brain to solve the cocktail party problem. A neural network model of auditory scene analysis, called the ARTSTREAM model, is presented to propose how the brain accomplishes this feat. The model clarifies how the frequency components that correspond to a given acoustic source may be coherently grouped together into a distinct stream based on pitch and spatial location cues. The model also clarifies how multiple streams may be distinguished and separated by the brain. Streams are formed as spectral-pitch resonances that emerge through feedback interactions between frequency-specific spectral representations of a sound source and its pitch. First, the model transforms a sound into a spatial pattern of frequency-specific activation across a spectral stream layer. The sound has multiple parallel representations at this layer. A sound's spectral representation activates a bottom-up filter that is sensitive to the harmonics of the sound's pitch. This filter activates a pitch category which, in turn, activates a top-down expectation that is also sensitive to the harmonics of the pitch. Resonance develops when the spectral and pitch representations mutually reinforce one another. Resonance provides the coherence that allows one voice or instrument to be tracked through a noisy multiple source environment. Spectral components are suppressed if they do not match harmonics of the top-down expectation that is read-out by the selected pitch, thereby allowing another stream to capture these components, as in the 'old-plus-new heuristic' of Bregman. Multiple simultaneously occurring spectral-pitch resonances can hereby emerge. These resonance and matching mechanisms are specialized versions of Adaptive Resonance Theory, or ART, which clarifies how pitch representations can self-organize during learning of harmonic bottom-up filters and top-down expectations. The model also clarifies how spatial location cues can help to disambiguate two sources with similar spectral cues. Data are simulated from psychophysical grouping experiments, such as how a tone sweeping upwards in frequency creates a bounce percept by grouping with a downward sweeping tone due to proximity in frequency, even if noise replaces the tones at their intersection point. Illusory auditory percepts are also simulated, such as the auditory continuity illusion of a tone continuing through a noise burst even if the tone is not present during the noise, and the scale illusion of Deutsch whereby downward and upward scales presented alternately to the two ears are regrouped based on frequency proximity, leading to a bounce percept. Since related sorts of resonances have been used to quantitatively simulate psychophysical data about speech perception, the model strengthens the hypothesis that ART-like mechanisms are used at multiple levels of the auditory system. Proposals for developing the model to explain more complex streaming data are also provided.

Acoustic Stimulation↗

PubMed2005

Sound level dependence of the primary auditory cortex: Simultaneous measurement with 61-channel EEG and fMRI.

Sound level dependence has been investigated for years with event-related potentials (ERP). A serotonergic modulation of the sound level dependence only of the primary auditory cortex but not of the auditory association cortex has been suggested by a number of clinical and preclinical studies. Therefore, a precise covering of the activity of the primary auditory cortex seems necessary if sound level dependence is used as an indicator of the central serotonergic system. Recent fMRI studies described a pronounced sound level dependence only in the Heschl gyrus/primary auditory cortex but not in auditory association areas. In the present simultaneous 61-channel EEG and fMRI study investigating fourteen healthy subjects, we found a high correlation between the loudness-dependent change of the extent of fMRI activation (number of activated voxels) and the corresponding changes of the mean current source density within the same region of interest covering the primary auditory cortex (r = 0.84, P < 0.001). Our findings suggest a close relationship between the fMRI signal and event-related potential activity. In addition, the correspondence of the ERP-based data and the fMRI results further supports the validity of the ERP localization approach.

Acoustic Stimulation↗

PubMed2005

Evidence of vibrotactile input to human auditory cortex.

Low frequency vibrations can be detected by both tactile and auditory systems. The aim of the present study is to find out, by means of whole-scalp magnetoencephalography (MEG), whether vibrotactile stimulation alone would activate human auditory cortical areas. We recorded MEG signals from eleven normal-hearing adults to 200-Hz vibrations (on average 19.5 dB above the individual tactile detection threshold), delivered to right-hand fingertips. All subjects reported a perception of a sound when they touched the vibrating tube, and they reported to perceive nothing when not touching the tube. The vibrotactile stimuli elicited clear and reproducible vibrotactile evoked fields (VTEFs) in ten subjects, whereas no MEG responses were observed when the tube was not touched. First responses to the vibrotactile stimuli, peaking around 60 ms, originated in the primary somatosensory cortex in all subjects. They were followed by activations in the auditory cortices, either bilaterally (N = 5) or unilaterally (N = 5), and by activations in the secondary somatosensory (SII) cortex, either contralaterally (N = 3) or ipsilaterally (N = 4). Both the SII and auditory activations consisted of transient responses at 100-200 ms. Additional auditory sustained activation was identified in nine subjects, either bilaterally (N = 2) or ipsilaterally (N = 7), at 200-700 ms. Our results suggest convergence of vibrotactile input to the auditory cortex in normal-hearing adults, in agreement with results previously obtained in a congenitally deaf adult.

Adult↗

PubMed2006

Touch activates human auditory cortex.

Vibrotactile stimuli can facilitate hearing, both in hearing-impaired and in normally hearing people. Accordingly, the sounds of hands exploring a surface contribute to the explorer's haptic percepts. As a possible brain basis of such phenomena, functional brain imaging has identified activations specific to audiotactile interaction in secondary somatosensory cortex, auditory belt area, and posterior parietal cortex, depending on the quality and relative salience of the stimuli. We studied 13 subjects with non-invasive functional magnetic resonance imaging (fMRI) to search for auditory brain areas that would be activated by touch. Vibration bursts of 200 Hz were delivered to the subjects' fingers and palm and tactile pressure pulses to their fingertips. Noise bursts served to identify auditory cortex. Vibrotactile-auditory co-activation, addressed with minimal smoothing to obtain a conservative estimate, was found in an 85-mm3 region in the posterior auditory belt area. This co-activation could be related to facilitated hearing at the behavioral level, reflecting the analysis of sound-like temporal patterns in vibration. However, even tactile pulses (without any vibration) activated parts of the posterior auditory belt area, which therefore might subserve processing of audiotactile events that arise during dynamic contact between hands and environment.

Adult↗

PubMed1999

Prefrontal connections of the parabelt auditory cortex in macaque monkeys.

In the present study, we determined connections of three newly defined regions of auditory cortex with regions of the frontal lobe, and how two of these regions in the frontal lobe interconnect and connect to other portions of frontal cortex and the temporal lobe in macaque monkeys. We conceptualize auditory cortex as including a core of primary areas, a surrounding belt of auditory areas, a lateral parabelt of two divisions, and adjoining regions of temporal cortex with parabelt connections. Injections of several different fluorescent tracers and wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) were placed in caudal (CPB) and rostral (RPB) divisions of the parabelt, and in cortex of the superior temporal gyrus rostral to the parabelt with parabelt connections (STGr). Injections were also placed in two regions of the frontal lobe that were labeled by a parabelt injection in the same case. The results lead to several major conclusions. First, CPB injections label many neurons in dorsal prearcuate cortex in the region of the frontal eye field and neurons in dorsal prefrontal cortex of the principal sulcus, but few or no neurons in orbitofrontal cortex. Fine-grain label in these same regions as a result of a WGA-HRP injection suggests that the connections are reciprocal. Second, RPB injections label overlapping prearcuate and principal sulcus locations, as well as more rostral cortex of the principal sulcus, and several locations in orbitofrontal cortex. Third, STGr injections label locations in orbitofrontal cortex, some of which overlap those of RPB injections, but not prearcuate or principal sulcus locations. Fourth, injections in prearcuate and principal sulcus locations labeled by a CPB injection labeled neurons in CPB and RPB, with little involvement of the auditory belt and no involvement of the core. In addition, the results indicated that the two frontal lobe regions are densely interconnected. They also connect with largely separate regions of the frontal pole and more medial premotor and dorsal prefrontal cortex, but not with the extensive orbitofrontal region which has RPB and STGr connections. The results suggest that both RPB and CPB provide the major auditory connections with the region related to directing eye movements towards stimuli of interest, and the dorsal prefrontal cortex for working memory. Other auditory connections to these regions of the frontal lobe appear to be minor. RPB has connections with orbitofrontal cortex, important in psychosocial and emotional functions, while STGr primarily connects with orbital and polar prefrontal cortex.

Animals↗

PubMed2001

Developmental impairment of auditory evoked N1/P2 component in rats undernourished in utero: its relation to brain serotonin activity.

In utero undernourishment produces an elevation of L-tryptophan and serotonin in the brain, including the auditory cortex (A1), such changes seem to be related to an increase in the free fraction (FFT) of plasma L-tryptophan that is transported into the brain through the blood-brain barrier, where it is taken up by serotonergic neurons for serotonin synthesis. Our observations support that FFT has a positive correlation with L-tryptophan (L-Trp) and serotonin levels in the auditory cortex (r=0.95 and 0.82, respectively). Interestingly, a decreased intensity dependence of the auditory evoked N1/P2 component was found in gestationally undernourished animals during their postnatal development. The N1/P2 component had a negative correlation (r=0.81) with A1 serotonin, such that it reflects changes in the neurotransmitter concentration. The present observations suggest a relevant role of serotonin in modulating the activity of the auditory cortex. Since the N1/P2 component is mainly associated with the activity of A1 neurons, it may well be that perception of auditory information is impaired during this developmental period, in the early undernourished animals, possibly affecting cognitive processes. This may be relevant to humans since low birth weight babies that also suffered gestational undernourishment (fetal-placental insufficiency) present an increase in plasma FFT from birth up to 3 months of age. These findings support that the plasma FFT and the intensity dependence of the auditory evoked N1/P2 component relate one another and may be markers of changes of the brain serotonergic activity.

Animals↗

PubMed2001

"Primitive intelligence" in the auditory cortex.

The everyday auditory environment consists of multiple simultaneously active sources with overlapping temporal and spectral acoustic properties. Despite the seemingly chaotic composite signal impinging on our ears, the resulting perception is of an orderly "auditory scene" that is organized according to sources and auditory events, allowing us to select messages easily, recognize familiar sound patterns, and distinguish deviant or novel ones. Recent data suggest that these perceptual achievements are mainly based on processes of a cognitive nature ("sensory intelligence") in the auditory cortex. Even higher cognitive processes than previously thought, such as those that organize the auditory input, extract the common invariant patterns shared by a number of acoustically varying sounds, or anticipate the auditory events of the immediate future, occur at the level of sensory cortex (even when attention is not directed towards the sensory input).

Auditory Cortex↗

PubMed1981

Patterns of habituation to electrical stimulation of reticular and auditory pathways.

Patterns of habituation of the orienting response to electrical stimulation of midbrain, thalamus, and cortical components of the primary auditory pathway and the ascending reticular system were studied in awake, freely mobile cats. Individual orienting responses to high-frequency stimulation of structures in the auditory pathway could not be distinguished from orienting responses to stimulation of reticular structures. However, with repeated presentations of the stimulus, the orienting response to auditory pathway stimulation habituated significantly faster than did the orienting response to stimulation of structures in the ascending reticular system. Within the auditory pathway, orienting to stimulation of the inferior colliculus, the medial geniculate body, or primary auditory cortex did not result in distinguishable patterns of habituation. Stimulation of parietal cortex resulted in habituation that occurred significantly slower than habituation to auditory cortex stimulation, and significantly faster than habituation to stimulation of the midbrain reticular formation or the centre median nucleus of the thalamus. These results are discussed with regard to a hypothetical arousal system that includes the brain stem reticular formation, the intralaminar nuclei of the thalamus, and parts of the parietal cortex.

Animals↗