Biomedical subjects

Richard A Reale

Publications and source records attributed to Richard A Reale.

3 recordsLinked to original sources

PubMed2003

Functional connections between auditory cortex on Heschl's gyrus and on the lateral superior temporal gyrus in humans.

Functional connections between auditory fields on Heschl's gyrus (HG) and the acoustically responsive posterior lateral superior temporal gyrus (field PLST) were studied using electrical stimulation and recording methods in patients undergoing diagnosis and treatment of intractable epilepsy. Averaged auditory (click-train) evoked potentials were recorded from multicontact subdural recording arrays chronically implanted over the lateral surface of the superior temporal gyrus (STG) and from modified depth electrodes inserted into HG. Biphasic electrical pulses (bipolar, constant current, 0.2 ms) were delivered to HG sites while recording from the electrode array over acoustically responsive STG cortex. Stimulation of sites along the mediolateral extent of HG resulted in complex waveforms distributed over posterolateral STG. These areas overlapped each other and field PLST. For any given HG stimulus site, the morphology of the electrically evoked waveform varied across the STG map. A characteristic waveform was recorded at the site of maximal amplitude of response to stimulation of mesial HG [presumed primary auditory field (AI)]. Latency measurements suggest that the earliest evoked wave resulted from activation of connections within the cortex. Waveforms changed with changes in rate of electrical HG stimulation or with shifts in the HG stimulus site. Data suggest widespread convergence and divergence of input from HG to posterior STG. Evidence is presented for a reciprocal functional projection, from posterolateral STG to HG. Results indicate that in humans there is a processing stream from AI on mesial HG to an associational auditory field (PLST) on the lateral surface of the superior temporal gyrus.

Acoustic Stimulation↗

PubMed2003

Directional sensitivity of neurons in the primary auditory (AI) cortex: effects of sound-source intensity level.

Transient sounds were delivered from different directions in virtual acoustic space while recording from single neurons in primary auditory cortex (AI) of cats under general anesthesia. The intensity level of the sound source was varied parametrically to determine the operating characteristics of the spatial receptive field. The spatial receptive field was constructed from the onset latency of the response to a sound at each sampled direction. Spatial gradients of response latency composing a receptive field are due partially to a systematic co-dependence on sound-source direction and intensity level. Typically, at any given intensity level, the distribution of response latency within the receptive field was unimodal with a range of approximately 3-4 ms, although for some cells and some levels, the spread could be as much as 20 or as little as 2 ms. Response latency, averaged across directions, differed among neurons for the same intensity level, and also differed among intensity levels for the same neuron. Generally, increases in intensity level resulted in decreases in the mean and variance, which follows an inverse Gaussian distribution. Receptive field models, based on response latency, are developed using multiple parameters (azimuth, elevation, intensity), validated with Monte Carlo simulation, and their spatial filtering described using spherical harmonic analysis. Observations from an ensemble of modeled receptive fields are obtained by linking the inverse Gaussian density to the probabilistic inverse problem of estimating sound-source direction and intensity. Upper bounds on acuity is derived from the ensemble using Fisher information, and the predicted patterns of estimation errors are related to psychophysical performance.

Acoustic Stimulation↗

PubMed2003

Likelihood approaches to sensory coding in auditory cortex.

Likelihood methods began their evolution in the early 1920s with R A Fisher, and have developed into a rich framework for inferential statistics. This framework offers tools for the analysis of the differential geometry of the full likelihood function based on observed data. We examine likelihood functions derived from inverse Gaussian (IG) probability density models of cortical ensemble responses of single units. Specifically, we investigate the problem of sound localization from the observation of an ensemble of neural responses recorded from the primary (Al) field of the auditory cortex. The problem is framed as a probabilistic inverse problem with multiple sources of ambiguity. Observed and expected Fisher information are defined for the IG cortical ensemble likelihood functions. Receptive field functions of multiple acoustic parameters are constructed and linked to the IG density. The impact of estimating multiple acoustic parameters related to the direction of a sound is discussed, and the implications of eliminating nuisance parameters are considered. We examine the degree of acuity afforded by a small ensemble of cortical neurons for locating sounds in space, and show the predicted patterns of estimation errors, which tend to follow psychophysical performance.

Acoustic Stimulation↗