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PubMedDate not supplied

Injury- and use-related plasticity in adult auditory cortex.

After restricted cochlear lesions in adult animals the frequency selectivity of neurons in the cortical region deprived of its normal input by the lesion is changed such that the region is occupied by expanded representations of adjacent (perilesion) frequencies. These changes reflect a dynamic process of reorganization (plasticity) and are not explicable as passive consequences of the lesion. Analogous plasticity of cortical frequency selectivity and organization is seen following behavioural training that enhances the significance of particular acoustic stimuli. The occurrence of injury- and use-related auditory cortical plasticity gives rise to a number of questions relating to the mechanisms involved, the perceptual consequences and functional significance of such plastic changes, and their implications for the central processing of input from prosthetic devices. Evidence relating to these issues is briefly summarized in this review, and the directions of future research are considered.

Auditory Cortex↗
PubMed1989

Evidence for a contribution of the auditory cortex to audiospinal facilitation in man.

Facilitation of the spinal monosynaptic reflex by auditory stimulation has been demonstrated previously in animals and man. Analysis of the time course of audiospinal facilitation (ASF) in normal subjects is reported. The role of the cerebral cortex in the control of audiospinal facilitation was investigated in 32 patients with anatomically well-circumscribed lesions, the precise topography of which was determined stereotaxically. Lesions of the caudal part (Heschl's gyrus and temporal plane) of the superior temporal gyrus selectively depressed ASF evoked by contralateral auditory stimulation. In contrast, lesions in temporal, parietal and occipital lobes had no effect. Results obtained with frontal lobe lesions were not homogeneous. The specific involvement of auditory cortex in the gating of behavioral audiomotor reactions is discussed.

Acoustic Stimulation↗
PubMed2006

Perception modulates auditory cortex activation.

Event-related functional magnetic resonance imaging signal change in Heschl's gyrus and the planum temporale was found to reflect sensory decisions about target presence. In a dichotic listening task, activation was higher for target present responses, irrespective of actual target presence. In fact, activation was highest for false alarms, that is, 'present' responses in the absence of a target stimulus, and lowest for missed targets. This shows that activity at the earliest stage of cortical auditory processing reflects subjective perceptual decisions. Whether this activation is driven by bottom-up or top-down factors remains to be investigated.

Acoustic Stimulation↗
PubMed1975

The association connexions of the suprasylvian fringe (SF) and other areas of the cat auditory cortex.

The association connexions of the peri-auditory (SF, Ea and INS) and auditory (AI, AII and Ep) areas of the cat cortex were studied in silver impregnated material of 32 experiments with cortical lesions. The cortex of the lateral bank of the rostral part of the middle suprasylvian sulcus (SF) sends many fibres to AI and to the insular cortex (INS), and has scanty projections upon AII and Ep. In addition, it sends fibres to the visual area 17 as well as to the ventral bank of the medial part of the cruciate sulcus. It receives fibres from the three auditory areas AI, AII and Ep, as well as from Ea and INS. The dorsal part of the anterior ectosylvian gyrus (Ea) projects upon SF, AI, and AII. Ea sends few fibres to Ep, and receives relatively dense projections from AI and AII. The anterior sylvian gyrus (INS) projects heavily upon AII as well as upon the superficial part of SF. It sends a few fibres also to Ep. INS receives heavy projections from AII and relatively lighter connections from SF, AI and Ep. The three auditory areas AI, AII and Ep are strongly mutually interconnected. AI and Ep have scanty projections upon the visual area 19, and AI also to the lateral suprasylvian visual area, as well as upon the ventral bank of the medial cruciate sulcus. Correlations of the association connexions with the functions of each area are discussed.

Animals↗
PubMed1991

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

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

Acoustic Stimulation↗
PubMed2004

Temporal dynamics of pitch in human auditory cortex.

Recent functional imaging studies have shown that sounds with temporal pitch produce selective activation in anterolateral Heschl's gyrus. This paper reports a magnetoencephalographic (MEG) study of the temporal dynamics of this activation. The cortical response specific to pitch was isolated from the intensity-related response in Planum temporale using a 'continuous stimulation' paradigm in which regular and irregular click trains alternate without interruption. The mean interclick interval (ICI) was 6, 12, 24, or 48 ms; the train length was 720 ms. The auditory sustained field serves as a level-dependent baseline that enhances the signal-to-noise ratio over previous techniques. The onset of pitch was accompanied by a prominent transient field, followed by a strong sustained field, both of which were associated with sources in lateral Heschl's gyrus. The sustained field rose from baseline about 70 ms after the onset of temporal regularity, asymptoted at about 450 ms, and commenced its return to baseline about 70 ms after pitch offset. The peak of the transient field occurred between 130 and 190 ms after regularity onset depending on the ICI. The latencies of the cortical pitch response are substantially longer than might be anticipated from temporal models of pitch perception. This finding suggests that the temporal integration associated with periodicity processing occurs in a subcortical structure, and that the cortical responses reflect subsequent processes involving the measurement of pitch values and changes in pitch.

Auditory Cortex↗
PubMed2006

Tuning to natural stimulus dynamics in primary auditory cortex.

The amplitude and pitch fluctuations of natural soundscapes often exhibit "1/f spectra", which means that large, abrupt changes in pitch or loudness occur proportionally less frequently in nature than gentle, gradual fluctuations. Furthermore, human listeners reportedly prefer 1/f distributed random melodies to melodies with faster (1/f0) or slower (1/f2) dynamics. One might therefore suspect that neurons in the central auditory system may be tuned to 1/f dynamics, particularly given that recent reports provide evidence for tuning to 1/f dynamics in primary visual cortex. To test whether neurons in primary auditory cortex (A1) are tuned to 1/f dynamics, we recorded responses to random tone complexes in which the fundamental frequency and the envelope were determined by statistically independent "1/f(gamma) random walks," with gamma set to values between 0.5 and 4. Many A1 neurons showed clear evidence of tuning and responded with higher firing rates to stimuli with gamma between 1 and 1.5. Response patterns elicited by 1/f(gamma) stimuli were more reproducible for values of gamma close to 1. These findings indicate that auditory cortex is indeed tuned to the 1/f dynamics commonly found in the statistical distributions of natural soundscapes.

Acoustic Stimulation↗
PubMed2005

Spectral and temporal processing in the human auditory cortex--revisited.

We use novel noise-like sound stimuli to identify cortical areas in which the functional magnetic resonance signal covaries with spectral and temporal acoustic complexity. The results support a model of hemispheric functional asymmetry for fine-grained spectral and fast temporal processing.

Acoustic Stimulation↗
PubMed1997

The role of the temporal coding system in the auditory cortex on speech recognition.

To elucidate the temporal coding system for speech recognition, we synthesized stimulation sounds which do not contain formant information but do contain temporal information by transforming original sound wave to click sequences. Using this stimulation sound, we performed a recognition test and used PET to examine the cortical activities in normal subjects listening to this sound. The results of the recognition test showed a good perception of the sounds made from sequential speech. The PET study demonstrated significant activation of the superior temporal gyri while listening to the stimulation speech sounds. Our results imply that these stimulation sounds were processed semantically in the auditory cortices. The temporal processing system is thought to make an important contribution to speech recognition.

Adult↗
PubMed2005

Responses to the purr call in three areas of the guinea pig auditory cortex.

Single electrodes were used to record from anaesthetized animals stimulated with a closed sound system. Neural responses to the purr call were very different in the dorsocaudal core field and in two long-latency belt areas, the ventrorostral belt and the dorsocaudal belt. Responses in the dorsocaudal core field were accurately timed to the start of the nine rhythmic pulses within the purr while the ventrorostral belt responses were more sustained and less temporally precise and most dorsocaudal belt units did not respond. These results are consistent with the separate processing of narrow-band tonal stimuli such as the purr by a ventrorostral pathway involving the primary auditory area and the ventrorostral belt but not by a dorsocaudal pathway from the dorsocaudal core field to the dorsocaudal belt area.

Acoustic Stimulation↗