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PubMed1995

Increased neuronal firing in the rat auditory cortex associated with preparatory set.

Extracellular single neuronal firings were recorded in the auditory cortex of rats (n = 4) performing a visual reaction-time task with a warning tone (10 kHz, 10 ms duration), which preceded the imperative light stimulus by an interstimulus interval (ISI) of 1.4 s. Thirty-six neuronal firings were evoked by the warning tone, with the peak latency being between 15 and 55 ms. Among them, nine neurons (25%) showed an increased firing frequency following the evoked response during the ISI, which was, in average, 2.5 times as high as the firing frequency during the baseline period. When the tones were presented independent of the imperative stimulus, such sustained increase in neuronal firing was not observed. Activation of the sensory cortex during the ISI may constitute one of the neuronal modulations related to preparatory set.

Acoustic Stimulation↗
PubMed1980

Acoustic responses after total destruction of the cochlear receptor: brainstem and auditory cortex.

Acoustically evoked neural activity has been recorded from the brainstem and auditory cortex of guinea pigs after complete destruction of the organ of Corti by the aminoglycosidic antibiotic amikacin. These responses to sound differ in important respects from the evoked potentials normally recorded from the auditory pathways. At the brainstem level they resemble the potentials reported by others after stimulation of the vestibular nerve.

Acoustic Stimulation↗
PubMed2004

The effects of aging in the medial geniculate nucleus: a comparison with the inferior colliculus and auditory cortex.

A common problem among the elderly is a difficulty in discriminating speech. One factor that may contribute to this is deterioration in the ability to process the dynamic components of speech such as formant transitions. The frequency-modulated (FM) sweep is a useful stimulus for investigating the neural basis of temporal processing speed since it has features in common with formant transitions. Previously, we showed that when cells in the auditory cortex of aged animals were presented with FM sweeps, they exhibited a decrease in temporal processing speed when compared to cells recorded from young animals. However, this was not the case for cells in the inferior colliculus (IC) where neural responses did not appear to be affected by aging. One question that remains is how the auditory thalamus is affected by aging: Is it similar to that of the auditory cortex or of the IC. To this end, single units were recorded from the ventral division of the medial geniculate nucleus (MGNv) of young and aged anaesthetized rats in response to FM sweeps. Results showed that there were no age-related differences in speed or direction selectivity of FM sweep responses in the MGNv. When compared with units recorded from the IC and AI, the responses of MGNv neurons were similar to those of the IC. This suggests that temporal processing speed is affected by aging in the cortex, but not in the auditory thalamus or midbrain.

Acoustic Stimulation↗
PubMed1975

[Correlation of potentials evoked by tones and clicks during simultaneous recording from many points in the auditory cortex of awake cats].

In unanaestheized cats the vooked potentials to various tones and clicks er simultaneosly recorded at 7 auditory and 1-2 somatosensory cortical points. The comparions of the evoked potentials to pure tones of equal lodness ranging from 250 to 7000 Hz showed no common cortical tonotpic distribuion. However there is an individual dependence of the potential components on the soung pitch and location of the recording point in the auditory cortex. The knonwn evoked poteintial dependence on sound intensity was confirmed and more developed regularity of this relation was revelead. With a change in sound intensity the absoulte and relative mangnitude alterations in all the potential components were observed...

Acoustic Stimulation↗
PubMed2005

Coupling between neuronal firing, field potentials, and FMRI in human auditory cortex.

Functional magnetic resonance imaging (fMRI) is an important tool for investigating human brain function, but the relationship between the hemodynamically based fMRI signals in the human brain and the underlying neuronal activity is unclear. We recorded single unit activity and local field potentials in auditory cortex of two neurosurgical patients and compared them with the fMRI signals of 11 healthy subjects during presentation of an identical movie segment. The predicted fMRI signals derived from single units and the measured fMRI signals from auditory cortex showed a highly significant correlation (r = 0.75, P < 10(-47)). Thus, fMRI signals can provide a reliable measure of the firing rate of human cortical neurons.

Adult↗
PubMed2006

The ferret auditory cortex: descending projections to the inferior colliculus.

Descending corticofugal projections are thought to play a critical role in shaping the responses of subcortical neurons. Here, we examine the origins and targets of ferret auditory corticocollicular projections. We show that the ectosylvian gyrus (EG), where the auditory cortex is located, can be subdivided into middle, anterior, and posterior regions according to the pattern of cytochrome oxidase staining and immunoreactivity for the neurofilament antibody SMI32. Injection of retrograde tracers in the inferior colliculus (IC) labeled large layer V pyramidal cells throughout the EG and adjacent sulci. Each region of the EG has a different pattern of descending projections. Neurons in the primary auditory fields in the middle EG project to the lateral nucleus (LN) of the ipsilateral IC and bilaterally to the dorsal cortex and dorsal part of the central nucleus (CN). The projection to these dorsomedial regions of the IC is predominantly ipsilateral and topographically organized. The secondary cortical fields in the posterior EG target the same midbrain areas but exclude the CN of the IC. A smaller projection to the ipsilateral LN also arises from the anterior EG, which is the only region of auditory cortex to target tegmental areas surrounding the IC, including the superior colliculus, periaqueductal gray, intercollicular tegmentum, and cuneiform nucleus. This pattern of corticocollicular connectivity is consistent with regional differences in physiological properties and provides another basis for subdividing ferret auditory cortex into functionally distinct areas.

Animals↗
PubMed2004

Responses of cat primary auditory cortex neurons to moving stimuli with dynamically changing interaural delays.

The spike responses of individual neurons in the primary auditory cortex were studied in anesthetized cats during exposure to stationary and moving stimuli with static or dynamically changing interaural delays (deltaT). Static stimuli were tones and clicks. Dynamic stimuli were created using series of synphase and antiphase clicks with interaural delays which changed over time. Sensitivity to changes in deltaT was predominantly present in neurons with low characteristic frequencies (less than 2.8 kHz). Changes in deltaT in moving stimuli induced responses in neurons sensitive to changes in deltaT in the stationary stimulus. The effect of movement could be a relationship between the level of spike activity and the direction and rate of change of deltaT or it could be a displacement of the tuning curve for the response to deltaT (the deltaT function) in the direction opposite to that of the direction of the change in deltaT. The magnitude of the effects of movement depended on the position of the period for changes in deltaT relative to the deltaT function. The greatest effects were seen with changes in deltaT on the sloping part of the deltaT function.

Acoustic Stimulation↗
PubMed2004

Evaluation of missing fundamental phenomenon in the human auditory cortex.

OBJECTIVE: Harmonic complex tones consisting of four or more continuous harmonics of a certain stem frequency are perceived as the pitch of the fundamental frequency tone, it is referred to as the missing fundamental phenomenon (MFP). It is considered that the MFP is produced in the central auditory system, not in the periphery. However, it remains unclear where and how complex sounds is integrated. Using 306ch magnetoencephalography (MEG), we investigated when and where the MFP was integrated in the auditory cortex. METHOD: We examined six subjects who were selected by MEG in 12 healthy right-handed adult volunteers with normal auditory sensation. Ears were randomly stimulated with five different complex tones consist of fundamental frequency tone and harmonic complex tones. The location and direction of equivalent current dipoles (ECD) were evaluated at P50 and N100 in the right temporal lobe by MEG. Dispersion of the source of ECD was respectively evaluated on their brain MRI. RESULTS: Stimulation of ears with harmonic complex tones and the stem frequency tone revealed the localization of P50 and N100 ECD in the transverse temporal gyrus and their peripheral superior temporal gyrus. Although the sources of P50 ECD for harmonic complex tones and the fundamental tone were varied around the transverse temporal gyrus and superior temporal gyrus, the sources of N100 ECD were almost identical at the transverse temporal gyrus, demonstrating the MFP. This phenomenon were similarly observed, even when dichotic listening were stimulated. CONCLUSION: These findings suggest that the MFP occurs in the transverse temporal gyrus and the superior temporal gyrus, which are the primary auditory cortex, between P50 and N100.

Acoustic Stimulation↗
PubMed1993

Rapid changes in the frequency tuning of neurons in cat auditory cortex resulting from pure-tone-induced temporary threshold shift.

The response areas (frequency by intensity) of single neurons in primary auditory cortex of anesthetized cats were studied before and after temporary threshold shifts in cochlear sensitivity induced by an intense pure tone. Cochlear temporary threshold shift was monitored through the threshold of the gross auditory nerve compound action potential and in most cases involved a notch-like loss centered at the characteristic frequency of the unit under study. Only two neurons showed changes in response area that mirrored the changes at the auditory periphery. Most neurons (14) showed more complex changes involving both expansion and contraction of response areas. Expansion of response areas was indicated by lower thresholds at some frequencies and by the emergence of sensitivity to previously ineffective frequencies. A change was classified as contraction when the response area after the intense-tone exposure was smaller than would be expected by applying the profile of the temporary threshold shift to the initial response area. Contraction of both upper (high intensity) and lower boundaries of response areas was found; in the most extreme cases, neurons were totally unresponsive after the intense-tone exposure. The complexity of effects of temporary threshold shifts on the response areas of cortical neurons is likely to be related to mechanisms that normally determine the frequency response limits of these neurons. The response areas of cortical neurons are more complex than those of auditory nerve fibers, and are thought to reflect the integration of excitatory and inhibitory inputs. The variety of effects observed in this study are consistent with the excitatory and inhibitory components of the response area of a given neuron being differentially affected by the temporary threshold shift.

Acoustic Stimulation↗
PubMed1975

A Golgi and electron microscopical study of nerve cells in layer I of the cat auditory cortex.

The nerve cells of the plexiform layer of the cat auditory cortex were studied in Golgi rapid preparations, and by electron microscopy. In the Golgi material 178 cells were found. Thirty were horizontal cells (Cajal's cells) with spiny dendrites and a long axon with horizontal trajectory. Seventy-two small cells had smooth dendrites and a short axon branching profusely around the perikaryon, within the plexiform layer. Twenty-eight were slightly larger cells, morphologically similar to the small ones, but their axons and dendrites were longer, extending to layer II. Twenty-five cells had large bottle-shaped perikarya, spiny dendrites reaching layer II, and a vertically oriented axon branching in layer II, and sometimes reaching layer III. In addition, 23 small modified pyramidal cells, similar to those of layer II, were found within the boundaries of layer I. In the most superficial 50 mum of the cortex horizontal cells were found, but the other categories were very rare. The 3 categories of short axon cells were preferentially localized between 50 and 150 mum from the pial surface. By electron microscopy two classes of cells were found. The first had abundant mitochondria, well defined Nissl bodies and few axosomatic synapses. The second had few mitochondria, undefined Nissl bodies and 6-8 axosomatic synapses per profile. Desmosome-like membrane specializations were found between perikarya of the second class and pyramidal dendrites or their spines. It is suggested that the first class of cells found by electron microscopy may correspond to the horizontal cells while the second class may correspond to the 3 categories of short axon cells.

Age Factors↗
PubMed2002

Intracellular characterization of suppressive responses in supragranular pyramidal neurons of cat primary auditory cortex in vivo.

Several suppressive processes shape the response properties of auditory neurons, namely lateral inhibition, non-monotonic rate level function and excitation/inhibition binaural interaction. By combining intracellular recording from and staining of layers 2 and 3 pyramidal neurons (PNs) in cat primary auditory cortex, we demonstrate the temporal aspects of depolarization and hyperpolarization underlying these suppressions using pure tone stimulation. Two populations can be distinguished by the occurrence of hyperpolarization following onset depolarization (O-DEP). In layer 2 PNs there is an absence of hyperpolarization following O-DEP, while in layer 3 PNs hyperpolarization follows O-DEP. The latency of O-DEP is shortest at the neuron's best frequency. The latency shortens as sound intensity increases. In non-monotonic PNs, hyperpolarization onset becomes shorter as sound intensity increases. This earlier onset of hyperpolarization shortens the duration of the preceding O-DEP, resulting in a decreased O-DEP amplitude. Diverse patterns in the temporal interaction of depolarization and hyperpolarization underlie the binaural suppression interaction. These results demonstrate that diverse suppressive responses result from differences in the temporal timing of excitation and inhibition. The present results also suggest the possibility of distinct connections between PNs responding in a similar manner.

Acoustic Stimulation↗
PubMed2007

Working memory specific activity in auditory cortex: potential correlates of sequential processing and maintenance.

Working memory (WM) tasks involve several interrelated processes during which past information must be transiently maintained, recalled, and compared with test items according to previously instructed rules. It is not clear whether the rule-specific comparisons of perceptual with memorized items are only performed in previously identified frontal and parietal WM areas or whether these areas orchestrate such comparisons by feedback to sensory cortex. We tested the latter hypothesis by focusing on auditory cortex (AC) areas with low-noise functional magnetic resonance imaging in a 2-back WM task involving frequency-modulated (FM) tones. The control condition was a 0-back task on the same stimuli. Analysis of the group data identified an area on right planum temporale equally activated by both tasks and an area on the left planum temporale specifically involved in the 2-back task. A region of interest analysis in each individual revealed that activation on the left planum temporale in the 2-back task positively correlated with the task performance of the subjects. This strongly suggests a prominent role of the AC in 2-back WM tasks. In conjunction with previous findings on FM processing, the left lateralized effect presumably reflects the complex sequential processing demand of the 2-back matching to sample task.

Adult↗
PubMed1988

Functional zones in the auditory cortex of the echolocating bat, Myotis lucifugus.

Neurophysiological mapping experiments in the auditory cortex of the frequency-modulated bat, Myotis lucifugus, reveal 3 functional subregions: a tonotopic zone located dorsally, a delay-sensitive zone more ventrally, and an intermediate zone of major overlap. The unique finding of an overlapping cortical region representing both spectral and time-delay information of echoes is intriguing in view of a recent behavioral study suggesting the convergence of such echo cues in auditory perception. (Simmons et al., Soc. Neurosci. Abstr., 13 [1987] 870).

Acoustic Stimulation↗
PubMed1996

Tonotopic mapping in auditory cortex of the chinchilla.

Using single-unit electrophysiological methods we have mapped sound frequency (or cochleotopic) representation in the auditory cortex of the chinchilla. We describe the surgical approach to expose this area. We report on maps from six subjects and note a considerable variation in shape between individuals. In general, the primary area has a cochleotopic/tonotopic organization in which low frequencies are represented rostrally and higher frequencies caudally. Neurons in the primary area have latency and tuning properties comparable to other mammalian species. A region anterior to the primary (AI) auditory are has a reverse tonotopic map and may be analogous to the anterior auditory field (AAF) reported in other species.

Acoustic Stimulation↗
PubMedDate not supplied

Characteristics of intracellularly injected infragranular pyramidal neurons in cat primary auditory cortex.

Pyramidal neurons in layers V and VI of cat primary auditory cortex (AI) were intracellularly injected with biocytin after functional characterization according to a position relative to an anteroposterior sequence of best-frequency responses. A sample of 19 completely filled neurons was analyzed, and a preliminary classification was made on the basis of dendritic morphology and axon collateral distribution. Layer V cells could be divided into two types. Cells in the upper part of layer V and projecting toward the diencephalon had a large cell body and an apical dendrite with extensive branches in layer I. These cells had few recurrent axon collaterals, and no terminal axonal bushes were formed in the vicinity of the dendritic field. Long horizontal collaterals with many boutons, however, extended in various directions parallel to the cortical surface. By contrast, cells in the lower part of layer V and sending an axon into the putamen, or without an obvious subcortical axon, had a medium soma and an apical dendrite with few branches in layer I. These cells had a dense bush of recurrent collaterals extending into layers II and III and surrounding the dendritic field, but few or no horizontal collaterals. Layer VI injected neurons were more heterogeneous. All had a thin ascending dendrite with oblique branches both ending in layer III. Axon collateral distributions varied from cell to cell. Relatively small cells with an apical dendrite that branched frequently in layers III and IV had a dense network of recurrent collaterals in the dendritic field, but virtually no horizontal collaterals. This type projected toward the diencephalon. Cells with relatively long horizontal collaterals and a weak recurrent system confined to layers V and VI had a unique arborization pattern of basal dendrites. This type may have projected to the claustrum or other cortical areas. One cell with dendritic branches restricted to layer VI had horizontal collaterals predominantly in layer VI. This cell projected into the corpus callosum. The apparent close correlation between extrinsic projections of infragranular neurons and their dendritic morphology and intracortical collateral distributions suggests that differentially projecting cells may engage different elements of intracortical circuitry in AI.

Animals↗
PubMed1997

Time course of forward masking tuning curves in cat primary auditory cortex.

Nonsimultaneous two-tone interactions were studied in the primary auditory cortex of anesthetized cats. Poststimulatory effects of pure tone bursts (masker) on the evoked activity of a fixed tone burst (probe) were investigated. The temporal interval from masker onset to probe onset (stimulus onset asynchrony), masker frequency, and intensity were parametrically varied. For all of the 53 single units and 58 multiple-unit clusters, the neural activity of the probe signal was either inhibited, facilitated, and/or delayed by a limited set of masker stimuli. The stimulus range from which forward inhibition of the probe was induced typically was centered at and had approximately the size of the neuron's excitatory receptive field. This "masking tuning curve" was usually V shaped, i.e., the frequency range of inhibiting masker stimuli increased with the masker intensity. Forward inhibition was induced at the shortest stimulus onset asynchrony between masker and probe. With longer stimulus onset asynchronies, the frequency range of inhibiting maskers gradually became smaller. Recovery from forward inhibition occurred first at the lower- and higher-frequency borders of the masking tuning curve and lasted the longest for frequencies close to the neuron's characteristic frequency. The maximal duration of forward inhibition was measured as the longest period over which reduction of probe responses was observed. It was in the range of 53-430 ms, with an average of 143 +/- 71 (SD) ms. Amount, duration and type of forward inhibition were weakly but significantly correlated with "static" neural receptive field properties like characteristic frequency, bandwidth, and latency. For the majority of neurons, the minimal inhibitory masker intensity increased when the stimulus onset asynchrony became longer. In most cases the highest masker intensities induced the longest forward inhibition. A significant number of neurons, however, exhibited longest periods of inhibition after maskers of intermediate intensity. The results show that the ability of cortical cells to respond with an excitatory activity depends on the temporal stimulus context. Neurons can follow higher repetition rates of stimulus sequences when successive stimuli differ in their spectral content. The differential sensitivity to temporal sound sequences within the receptive field of cortical cells as well as across different cells could contribute to the neural processing of temporally structured stimuli like speech and animal vocalizations.

Acoustic Stimulation↗
PubMed1983

Intensity difference thresholds assessed with eighth nerve and auditory cortex potentials: compared values from cochlear and vascular responses.

In normal guinea pigs the eighth nerve compound action potential shows a latency of about 1 ms and the evoked early potential at the auditory cortex occurs after about 10 ms. Determination of auditory sensitivity with both responses using tone-bursts of variable rise/fall time and plateau duration showed they are responses to the onset of the stimulus since the existence of a plateau has no effect. Increases in stimulus rise time diminish the synchrony of both responses, the limits were found to be 2 ms for eighth nerve responses and 10 ms for cortical potentials. Amplitude modulation of continuous tones using these time values evokes clear responses at levels which apparently correspond to intensity difference thresholds measured behaviorally by other authors. Similar measures were performed on saccular acoustic responses, using the model of selective cochlear destruction. Evoked responses could also be observed at levels of amplitude modulation similar to those of normal animals. This fine sensitivity reinforces the idea of a functionality of the saccular acoustic reception.

Action Potentials↗