Biomedical subjects

P Bedenbaugh

Publications and source records attributed to P Bedenbaugh.

7 recordsLinked to original sources

PubMed1997

Multiunit normalized cross correlation differs from the average single-unit normalized correlation.

As the technology for simultaneously recording from many brain locations becomes more available, more and more laboratories are measuring the cross-correlation between single-neuron spike trains, and between composite spike trains derived from several undiscriminated cells recorded on a single electrode (multiunit clusters). The relationship between single-unit correlations and multiunit cluster correlations has not yet been fully explored. We calculated the normalized cross-correlation (NCC) between single-unit spike trains and between small clusters of units recorded in the rat somatosensory cortex. The NCC between small clusters of units was larger than the NCC between single units. To understand this result, we investigated the scaling of the NCC with the number of units in a cluster. Multiunit cross-correlation can be a more sensitive detector of neuronal relationship than single-unit cross-correlation. However, changes in multiunit cross-correlation are difficult to interpret uniquely because they depend on the number of cells recorded on each electrode and because they can arise from changes in the correlation between cells recorded on a single electrode or from changes in the correlation between cells recorded on two electrodes.

Animals↗

PubMed1997

A primate model for studying focal dystonia and repetitive strain injury: effects on the primary somatosensory cortex.

BACKGROUND AND PURPOSE: Job-related repetitive strain injuries (RSIs) are increasing, and current treatment strategies often fail to return injured people to work. This study documented the neural consequences of using two different movement strategies for active, repetitive hand closing and opening. METHODS: Two owl monkeys were trained for 20 weeks to repetitively close a handpiece against an 80-g force (3-400 trials per day, training at 80%-90% accuracy). One monkey used a highly articulated hand-squeezing strategy, and the other monkey used a proximal arm-pulling strategy. Changes in motor performance were analyzed, and the electrophysiological maps of the hand representation on the trained primary sensory cortex (area 3b) were compared with those of untrained control animals and the untrained sides of the trained monkeys. RESULTS: The monkey using the articulated hand-squeezing strategy showed motor deterioration and dedifferentiation of the normally sharply segregated areas of the hand representation in area 3b. Mild degradation of the hand representation was measured in the monkey using the proximal arm-pulling strategy, but there was no motor dysfunction. CONCLUSION AND DISCUSSION: Attended, highly articulated, repetitive finger squeezing degrades the hand representation and interferes with motor control. A proximal, more variable repetitive strategy minimized the sensory degradation and preserved motor control. Restoring the hand representation may be a critical part of treatment for patients with chronic RSI and focal hand dystonia.

Animals↗

PubMed1994

Rectification of correlation by a sigmoid nonlinearity.

We investigated the normalized autocovariance (correlation coefficient) function of the output of an erf() function nonlinearity subject to non-zero mean Gaussian noise input. When the sigmoid is wide compared to the input, or the input mean is close to the midpoint of the sigmoid, the output correlation coefficient function is very close to the input correlation coefficient function. When the noise mean and variance are such that there is a significant probability of operating in the saturation region and the sigmoid is not too flat, the correlation coefficient of the output function is less than that of the input. This difference is much greater when the correlation coefficient is negative than when it is positive. The sigmoid partially rectifies the correlation coefficient function. The analysis does not depend on the spectral properties of the input noise. All that is required is that the input at times t and (t + tau) be jointly gaussian with the same mean and autocovariance. The analysis therefore applies equally well to the case of two identical sigmoids with jointly gaussian inputs. This correlational rectification could help explain the parameter sensitivity of "neural network" models. If biological neurons share this property it could explain why few negative correlations between spike trains have been observed.

Animals↗

PubMed1992

Intrinsic signal optical imaging in the forepaw area of rat somatosensory cortex.

The responses of somatosensory cortex (S-I) to tactile stimulation of the forepaw were assessed by intrinsic signal optical imaging. The tips of digits two or five were alternately touched with mechanical tappers while video photographs were taken of S-I illuminated by an 800-nm light source. The resulting images showed two highlighted areas about 300 microns in diameter and 500 microns apart. Generation of these images required less than 1 hr. Electrode penetrations placed in the areas highlighted during stimulation provided multiunit recordings with receptive fields appropriate for the stimulated digit and not the other digit. Penetrations between the high-lighted areas yielded receptive fields on intervening digits. These results demonstrate that intrinsic signal optical images are obtainable in S-I and confirm the functional somatotopy previously reported using electrical recording. Furthermore, the short time required to produce the images and the obtainable spatial resolution suggest that optical recording could be employed for the study of cortical reorganization in this brain region.

Animals↗

PubMed1989

Neuronal assemblies.

This paper examines the concept of neuronal assembly as it has appeared in selected portions of the literature. The context is experimental access to real neuronal assemblies in working brains, as made possible by recent technological progress. One current measure of assembly organization is based on correlation of firing among neurons; recent observations show that such correlations can vary rapidly. In this paper, we demonstrate that dynamic firing correlation can be caused either by dynamic changes in neuronal connection strengths or, alternatively, by the effects of an unobserved (large) pool of other neurons. The static connectivity within the pool appears to be important in determining these effects.

Animals↗

PubMed1984

Dorsal root rhizotomy and avulsion in the cat: a comparison of long term effects on dorsal horn neuronal activity.

We performed an extracellular microelectrode analysis of the neuronal activity of cells located in deeper laminae of dorsal horns that had been deafferented by ipsilateral lumbar dorsal root rhizotomy or avulsion. Special attention was given to those cells that were recorded in preparations that were more than 6 weeks chronic. We compared the results to those obtained in nondenervated controls and in experiments in which the spinal cord was acutely transected at a midthoracic level, but had intact dorsal roots. There was an increase in ipsilateral flank and contralateral input in the chronically deafferented as compared to nondenervated controls. Differences were observed between long term rhizotomized and avulsed dorsal horns. Receptive fields extended on to flank and thoracic dermatomes after rhizotomy, often requiring only light cutaneous stimuli. Receptive fields were more restricted with avulsion injury, generally requiring moderate to strong, superficial or deep pinch. Histological analysis revealed consistent differential damage to the medial portion of Lissauer's tract with avulsion injury and subsequently more gliosis in the substantia gelatinosa. The loss of this propriospinal pathway may explain the lack of receptive field expansion on to the thoracic dermatomes and the stronger natural stimuli that were required. A higher percentage of cells with bilateral and inhibitory receptive fields was found in experiments in which the spinal cord was transected at a midthoracic level than in the controls. Ipsilateral excitatory receptive fields were also expanded as compared with control observations, but were not found on the flank.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1983

Stereotactic radiofrequency lesion making.

The physical principles of radiofrequency (RF) lesion making in stereotactic neurosurgery are summarized. Empirical data are given on the relationship between lesion size and lesioning parameters. Currently accepted ranges of lesioning parameters for selected stereotactic procedures are discussed. Advanced RF lesion electrode designs are described which improve the capabilities to reach and confirm targets.

Electrocoagulation↗