Biomedical subjects

G L Gerstein

Publications and source records attributed to G L Gerstein.

At least 19 recordsLinked to original sources

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↗

PubMed1992

Respiratory-related neural assemblies in the brain stem midline.

1. The initial objective of this study was to determine whether respiratory-related neural assemblies exist in the brain stem midline. A second goal was to seek evidence for concurrent relationships among the neurons that could generate the detected synchrony. 2. Experiments were conducted on anesthetized, paralyzed, bilaterally vagotomized, artificially ventilated cats. Spike trains of four to nine simultaneously monitored neurons were recorded in the regions of n. raphe obscurus-n. raphe pallidus and n. raphe magnus. 3. Data were analyzed with cycle-triggered histograms, cross-correlograms, snowflakes, and the gravitational representation. A significance test for the gravity method was developed and tested with spike trains generated by simulated networks with defined connections. 4. Ninety-three groups of neurons from 24 cats were studied. Thirty-nine groups from 19 cats included neurons that discharged synchronously on a millisecond time scale; less than or equal to 19 pairs of synchronously discharging neurons were found in one group. Twenty-seven of these 39 groups included neurons that had respiratory-modulated firing rates and discharged synchronously with other group members. Synchronous assemblies included cells monitored at rostral or caudal locations, or both. 5. Six classes of relationships were inferred from groups of neurons with multiple correlations: divergence (n = 11); convergence (n = 7); connections with opposite actions between neurons (n = 5); projections of synchronous neurons to separate targets (n = 5); projections to one neuron in a synchronous group (n = 4); and projections between two synchronous groups with common elements (n = 6). 6. The results document the existence of assemblies of synchronously discharging respiratory-related neurons in midline regions of the brain stem and suggest that divergent excitatory and inhibitory connections within the midline participate in the generation of that synchrony. Links between assemblies may operate to stabilize their collective activity in a particular state.

Afferent Pathways↗

PubMed1992

Dynamic reconfiguration of brain stem neural assemblies: respiratory phase-dependent synchrony versus modulation of firing rates.

1. The objective of this work was to determine whether configurations of midline brain stem neural assemblies change during the respiratory cycle. 2. Spike trains of several single neurons were recorded simultaneously in anesthetized, paralyzed, bilaterally vagotomized, artificially ventilated cats. Data were analyzed with cross-correlational and gravity methods. 3. Sequential samples from each of eight groups of neurons known to contain synchronously discharging neurons exhibited temporal variations in that synchrony. 4. Gravity analysis of short (less than 200-s) samples of spike train data revealed 20 pairs of clustered particles that were not predicted from cross-correlation analysis of the parent data sets (greater than 20 min). 5. Twenty-nine groups of three to eight simultaneously monitored neurons, each with at least two synchronously discharging neurons, were analyzed for evidence of respiratory phase-dependent modulation of that coordinated activity. Spikes from successive interleaved inspiratory and expiratory intervals were analyzed separately. 6. Neurons pairs in 11 groups were more synchronous during the inspiratory interval; six groups had pairs that were more synchronous during the expiratory period. In two groups, different pairs were synchronous in different respiratory phases. In 11 of the 26 pairs that exhibited phase-dependent differences in synchrony, neither neuron had a respiratory-modulated firing rate as judged by either the cycle-triggered histogram or an analysis of variance of their firing rates. 7. Configurations of respiratory-related brain stem neural networks changed with time and the phases of breathing. Neurons with no apparent respiratory modulation of their individual firing rates collectively exhibited respiratory phase-dependent modulation of their impulse synchrony.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Underestimation of visual texture slant by human observers: a model.

The perspective image of an obliquely inclined textured surface exhibits shape and density distortions of texture elements which allow a human observer to estimate the inclination angle of the surface. However, it has been known since the work of Gibson (1950) that, in the absence of other cues, humans tend to underestimate the slant angle of the surface, particularly when the texture is perceived as being "irregular." The perspective distortions which affect texture elements also shift the projected spatial frequencies of the texture in systematic ways. Using a suitable local spectral filter to measure these frequency gradients, the inclination angle of the surface may be estimated. A computational model has been developed which performs this task using distributions of outputs from filters found to be a good description of simple-cell receptive fields. However, for "irregular" textures the filter output distributions are more like those of "regular" textures at shallower angles of slant, leading the computational algorithm to underestimate the slant angle. This behavioral similarity between human and algorithm suggests the possibility that a similar visual computation is performed in cortex.

Algorithms↗

PubMed1991

Cross-talk theory of memory capacity in neural networks.

The present paper presents a theory for the mechanics of cross-talk among constituent neurons in networks in which multiple memory traces have been embedded, and develops criteria for memory capacity based on the disruptive influences of this cross-talk. The theory is based on interconnection patterns defined by the sequential configuration model of dynamic firing patterns. The theory accurately predicts the memory capacities observed in computer simulated nets, and predicts that cortical-like modules should be able to store up to about 300-900 selectively retrievable memory traces before disruption by cross-talk is likely. It also predicts that the cortex may has designed itself for modules of 30,000 neurons to at least in part to optimize memory capacity.

Animals↗

PubMed1991

Functional interactions among neurons in inferior temporal cortex of the awake macaque.

Functional interactions among inferior temporal cortex (IT) neurons were studied in the awake, fixating macaque monkey during the presentation of visual stimuli. Extracellular recordings were obtained simultaneously from several microelectrodes, and in many cases, spike trains from more than one neuron were extracted from each electrode by the use of spike shape sorting technology. Functional interactions between pairs of neurons were measured using cross-correlation. Discharge patterns of single neurons were evaluated using auto-correlation and PST histograms. Neurons recorded on the same electrode (within about 100 microns) had more similar stimulus selectivity and were more likely to show functional interactions than those recorded on different electrodes spaced about 250 to 500 microns apart. Most neurons tended to fire in bursts tens to hundreds of milliseconds in duration, and asynchronously from the stimulus induced rate changes. Correlated neuronal firing indicative of shared inputs and direct interactions was observed. Occurrence of shared input was significantly lower for neuron pairs recorded on different electrodes than for neurons recorded on the same electrode. Direct connections occurred about as often for neurons on different electrodes as for neurons on the same electrode. These results suggest that input projections are usually restricted to less than 500 micron patches and are then distributed over greater distances by intrinsic connections. Measurements of synaptic contribution suggest that typically more than 5 near-simultaneous inputs are required to cause an IT neuron to discharge.

Animals↗

PubMed1990

Dynamic temporal properties of effective connections in rat dorsal cochlear nucleus.

In a prior report we presented evidence that functionally connected dorsal cochlear nucleus (DCN) neurons in close proximity can show differing peristimulus time histograms (PSTHs) in response to the same stimulus. We wished to further investigate how interconnections between such neurons might participate in the PSTH patterns. Methodology has recently been developed which permits measurement of rapid changes in effective connectivity between neuron pairs: the normalized joint PSTH. Using this technique we have observed that rapid changes in effective connectivity do occur in the DCN. These observations demonstrate that the effects of one DCN neuron on another cannot necessarily be understood by sequential recordings from single units, even if anatomical connectivity can be established.

Acoustic Stimulation↗

PubMed1989

Coordinated activity of neuron pairs in anesthetized rat dorsal cochlear nucleus.

We have recorded from small groups of neurons in the dorsal cochlear nucleus of anesthetized rats in an effort to study neuronal interactions. Multi-unit recordings on each single electrode were sorted by waveform into spike trains from individual neurons using a principal components spike sorter. Pairs of such sorted spike trains were studied with cross-correlation analysis to detect excitatory and/or inhibitory interactions. In a few cases recordings were obtained from two electrodes simultaneously, thus allowing cross-correlation studies without the consequences of spike train waveform sorting. All neurons were characterized by their strongest response frequency (at a fixed sound pressure level) and peristimulus histogram responses to 55 ms tone bursts. Fifty-eight percent of the neuron pairs studied showed peaks in their cross-correlograms indicative of coordinated neural activity. Of these pairs, 86% showed peak configurations (i.e. correlograms with asymmetrically located peaks) consistent with the interpretation that one cell induced the other to discharge. The remaining correlograms contained symmetric peaks which were centrally located, possibly due to shared input to these neuron pairs. Latencies of asymmetric peaks in cross-correlograms were typically 2 ms; consequently, an intervening excitatory synapse may be involved. Similar results were obtained from at least one pair of neurons where each neuron was recorded by a separate electrode. Strongest response frequencies of each neuron pair, for which they could be determined, were within 0.17 log units. Peristimulus histograms from each neuron in these pairs revealed that it was common for adjacent cells to respond with differing time patterns under the same stimulus conditions. The variations in histogram patterns of interconnected neurons suggests some relatively complex integrative function for these circuits.

Acoustic Stimulation↗

PubMed1989

Gravitational representation of simultaneously recorded brainstem respiratory neuron spike trains.

Experiments designed to study concurrent processes in neural networks have been hampered by limitations of available analytical methods. A recently described gravitational representation of spike train data was used to evaluate groups of simultaneously monitored medullary respiratory related neurons in anesthetized, vagotomized cats. The results establish that the method can detect and define functional associations among elements of such groups after as few as 20 respiratory cycles.

Action Potentials↗

PubMed1989

A low-cost single-board solution for real-time, unsupervised waveform classification of multineuron recordings.

We describe a low-cost single-board system for unsupervised, real-time spike sorting of recordings from a number of neurons on a single microelectrode. The maximum number of spike classes depends on the quality of the recording; it will typically be between 2 and 5. The spike sorter communicates with a conventional microcomputer through a standard serial port (RS232). For typical firing rates as measured in the mammalian central nervous system, this set-up will accommodate up to some 10 parallel spike sorters for as many separate microelectrodes.

Algorithms↗

PubMed1989

Spectral time-course analysis of firing patterns in the dorsal cochlear nucleus.

Many previous studies of central auditory neurons have involved independent analyses of spectral and temporal response properties. The spectral response analysis is useful for defining the frequency and intensity regions over which a neuron is excited or inhibited. However, the conventional spectral response analysis only defines this distribution for the synaptic polarity (excitation or inhibition) which dominates the duration of the response. PST histograms of dorsal cochlear nucleus neurons however, often exhibit both excitatory and inhibitory (i.e. pause) components. The distribution of these transient pause intervals may in turn be highly dependent on stimulus parameters suggesting that the spectral area of excitation and inhibition, when considered in terms of short time frames, may be time-dependent. We performed a temporal analysis of the spectral response areas of neurons in the rat dorsal cochlear nucleus and present here an example based on a neuron showing distinct pauser and buildup responses in its PST histograms. The resulting analysis yielded a time course of the spectral response area which indicates that the transient periods of inhibition may have the effect of narrowing the bandwidth of excitation during the early portion of stimulation. Possible implications of this time course are discussed in relation to the narrower tuning that cochlear nucleus neurons often display in response to frequency sweeps than to pure tones.

Acoustic Stimulation↗

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↗

PubMed1989

Dynamics of neuronal firing correlation: modulation of "effective connectivity".

1. We reexamine the possibilities for analyzing and interpreting the time course of correlation in spike trains simultaneously and separably recorded from two neurons. 2. We develop procedures to quantify and properly normalize the classical joint peristimulus time scatter diagram. These allow separation of the "raw" correlation into components caused by direct stimulus modulations of the single-neuron firing rates and those caused by various types of interaction between the two neurons. 3. A newly developed significance test ("surprise") is applied to evaluate such inferences. 4. Application of the new procedures to simulated spike trains allowed the recovery of the known circuitry. In particular, it proved possible to recover fast stimulus-locked modulations of "effective connectivity," even if they were masked by strong direct stimulus modulations of individual firing rates. These procedures thus present a clearly superior alternative to the commonly used "shift predictor." 5. Adopting a model-based approach, we generalize the classical measures for quantifying a direct interneuronal connection ("efficacy" and "contribution") to include possible stimulus-locked time variations. 6. Application of the new procedures to real spike trains from several different preparations showed that fast stimulus-locked modulations of "effective connectivity" also occur for real neurons.

Animals↗

PubMed1988

Cortical auditory neuron interactions during presentation of 3-tone sequences: effective connectivity.

The role of cat's primary auditory cortex (AI) in both pattern discrimination and sound localization has been demonstrated by observing that ablations of it disrupt these functions. This research studied effective connectivity variations as a function of modifications in the temporal pattern of acoustic stimulation. Recordings of 10-15 neurons (simultaneously and separably) were made in AI of sedated cats. A bundle of 7 microelectrodes was stereotaxically placed along a tangential path. Stimuli were permutations of 3-tone bursts sequences. Each recorded neuron pair was analyzed off-line by cross-correlation. Cross-correlation of spike trains from neuron pairs showed signatures of direct and/or shared input. These appeared individually or in combination and for most pairs were present in spontaneous conditions. However, in stimulated conditions these spontaneous interactions were strongly modulated. The analysis detected differences in neuronal interaction during presentation of different tones. Similar differences occurred during presentation of any single particular stimulus if there was a history of different immediately previous tones. When individual neuron pair cross-correlations were put together to form an effective connectivity diagram among all recorded neurons, they turned out as different diagrams for different stimulus conditions.

Acoustic Stimulation↗

PubMed1988

On the significance of correlations among neuronal spike trains.

We consider several measures for the correlation of firing activity among different neurons, based on coincidence counts obtained from simultaneously recorded spike trains. We obtain explicit formulae for the probability distributions of these measures. This allows an exact, quantitative assessment of significance levels, and thus a comparison of data obtained in different experimental paradigms. In particular it is possible to compare stimulus-locked, and therefore time dependent correlations for different stimuli and also for different times relative to stimulus onset. This allows to separate purely stimulus-induced correlation from intrinsic interneuronal correlation. It further allows investigation of the dynamic characteristics of the interneuronal correlation. For the display of significance levels or the corresponding probabilities we propose a logarithmic measure, called "surprise".

Animals↗

PubMed1988

Unsupervised waveform classification for multi-neuron recordings: a real-time, software-based system. I. Algorithms and implementation.

We describe a new, mostly software-based device for the sorting of waveforms in an extracellular multi-neuron recording situation. The sorting algorithm is largely unattended, and, after an initial 'learning' process, works in real time. Shape comparisons are based on up to 8 time points in the waveform; these points (the reduced feature set) are chosen automatically by analyzing the current incoming data stream. A feasibility version has been implemented on a LSI-11/2 system, using FORTRAN for set-up calculations and assembler for the real-time operations. Detailed comparisons with performance of other sorting devices are presented in the companion paper.

Algorithms↗

PubMed1988

Unsupervised waveform classification for multi-neuron recordings: a real-time, software-based system. II. Performance comparison to other sorters.

The companion paper has described a new, fully automatic device for the sorting of action potential waveforms in real time. We present here a brief comparison of performance between this new device and several of the older, more traditional devices used for this purpose. We include in the comparison the performance of 3 human observers.

Algorithms↗

PubMed1988

Detecting spatiotemporal firing patterns among simultaneously recorded single neurons.

1. A particular firing pattern among simultaneously observed neurons represents a particular sequence of activity. If any multineuron pattern repeats significantly more than expected by chance, we may be observing a repeated state of a neural assembly as it processes similar units of information. 2. We present here an algorithm that rapidly finds all single or multineuron patterns that repeat two or more times within a block of data, as well as equations for calculating the number of patterns of given length and repetition that would be expected. The complexity of patterns for which it is practical to compute expected numbers is three to six spikes (inclusive). 3. Confidence limits are based on these expected numbers of patterns, so that is possible to identify groups of patterns that are worthy of further analysis. 4. These methods are tested against simulated multineuron data that has various types of known nonstationarities, with good agreement between observed and expected values. 5. Application to real spike trains shows a large excess of observed repeating patterns, of which some, but not all, are shown to be due to bursts of high frequency firing. 6. It should be possible to apply the new method as a filter in real time in order to search for an association between repeated pattern events and externally observable events (stimulus, behavior, etc.). Any repeated pattern events which cannot be so associated may represent a new indicator of internal events in the nervous system.

Algorithms↗