Encoding of sound-source location and movement: activity of single neurons and interactions between adjacent neurons in the monkey auditory cortex.

1. Neuronal mechanisms for decoding sound azimuth and angular movement were studied by recordings of several single units in parallel in the core areas of the auditory cortex of the macaque monkey. The activity of 180 units was recorded during the presentation of moving and static sound stimuli. Both the activity of single units and the interactions between neighboring neurons in response to each stimulus were analyzed. 2. Sixty-two percent of the units showed significant modulation of their firing rates as a function of the stimulus azimuth. Contralateral stimuli were preferred by the majority (approximately 60%) of these neurons. Thirty-five percent of the units showed mild but statistically significant modulation of their firing rates, which was specifically attributed to the angular movement of the sound source. 3. Eighty-nine percent of the "movement-sensitive" units were also "azimuth sensitive." The sound source's azimuth determined the pattern of the response components (on, sustained, off), whereas the source's movement affected only the magnitude of these components, typically the sustained component. Most neurons for which the sustained response to static sounds was greater for contralateral than ipsilateral stimuli preferred moving sounds that were moving into the contralateral hemifield. 4. Cross-correlation analysis was carried out for 245 neuron pairs. Cross-correlograms were computed for each pair under all stimulus conditions to allow comparison of the neuronal interactions under the various conditions. The shapes of some correlograms (after subtraction of direct stimulus effects) were dependent on specific stimulus conditions, suggesting that the effective connectivity between these neurons depended on the location and/or movement of the sound stimuli. Furthermore, joint peristimulus time (JPST) analysis indicated that modifications of connectivity may be temporally related to the stimulus and may occur over short periods of time. These results could not have been predicted from analysis of the independent single-unit responses to the stimuli. 5. The data suggest that both firing rates and correlated activity between adjacent neurons in the auditory cortex encode sound location and movement.

[1]  G. P. Moore,et al.  Neuronal spike trains and stochastic point processes. II. Simultaneous spike trains. , 1967, Biophysical journal.

[2]  Juhani Hyva¨rinen,et al.  Auditory cortical neurons in the cat sensitive to the direction of sound source movement , 1974 .

[3]  G L Gerstein,et al.  Interactions between neurons in auditory cortex of the cat. , 1974, Journal of neurophysiology.

[4]  D. Perrott,et al.  Minimum auditory movement angle: binaural localization of moving sound sources. , 1977, The Journal of the Acoustical Society of America.

[5]  Bryan E. Pfingst,et al.  A vertical stereotaxic approach to auditory cortex in the unanesthetized monkey , 1980, Journal of Neuroscience Methods.

[6]  D. A. Benson,et al.  Single-unit activity in the auditory cortex of monkeys actively localizing sound sources: Spatial tuning and behavioral dependency , 1981, Brain Research.

[7]  W. Jenkins,et al.  Sound localization: effects of unilateral lesions in central auditory system. , 1982, Journal of neurophysiology.

[8]  Ron D. Frostig,et al.  The effects of stimuli on the activity and functional connectivity of local neuronal groups in the cat auditory cortex , 1983, Brain Research.

[9]  D. Grantham.  Auditory spatial resolution under static and dynamic conditions , 1985 .

[10]  D W Grantham,et al.  Detection and discrimination of simulated motion of auditory targets in the horizontal plane. , 1986, The Journal of the Acoustical Society of America.

[11]  M Abeles,et al.  Temporal firing patterns of single units, pairs and triplets of units in the auditory cortex. , 1987, Israel journal of medical sciences.

[12]  S. Mateeff,et al.  Dynamic auditory localization: perceived position of a moving sound source. , 1988, Acta physiologica et pharmacologica Bulgarica.

[13]  Michael Erb,et al.  Functional connectivity in neuronal systems: Context-dependence of effective network organization does not require synaptic plasticity , 1989 .

[14]  M K Habib,et al.  Dynamics of neuronal firing correlation: modulation of "effective connectivity". , 1989, Journal of neurophysiology.

[15]  T. Imig,et al.  Single-unit selectivity to azimuthal direction and sound pressure level of noise bursts in cat high-frequency primary auditory cortex. , 1990, Journal of neurophysiology.

[16]  L. Aitkin,et al.  Azimuthal sensitivity of neurons in primary auditory cortex of cats. I. Types of sensitivity and the effects of variations in stimulus parameters. , 1990, Journal of neurophysiology.