Biomedical subjects

E Ahissar

Publications and source records attributed to E Ahissar.

24 records · Page 2Linked to original sources

PubMed1992

Dependence of cortical plasticity on correlated activity of single neurons and on behavioral context.

It has not been possible to analyze the cellular mechanisms underlying learning in behaving mammals because of the difficulties in recording intracellularly from awake animals. Therefore, in the present study of neuronal plasticity in behaving monkeys, the net effect of a single neuron on another neuron (the "functional connection") was evaluated by cross-correlating the times of firing of the two neurons. When two neurons were induced to fire together within a short time window, the functional connection between them was potentiated, and when simultaneous firing was prevented, the connection was depressed. These modifications were strongly dependent on the behavioral context of the stimuli that induced them. The results indicate that changes in the temporal contingency between neurons are often necessary, but not sufficient, for cortical plasticity in the adult monkey: behavioral relevance is required.

Acoustic Stimulation↗

PubMed1992

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.

Acoustic Stimulation↗

PubMed1991

Neural interactions in the frontal cortex of a behaving monkey: signs of dependence on stimulus context and behavioral state.

In order to gain an understanding of the processes taking place within and between neuronal assemblies, we made simultaneous recordings of spike trains from groups of up to 11 neurons in the frontal cortex of a rhesus monkey, that was trained to perform a sensorimotor behavioral task. We report here on preliminary results from correlation analysis of these neuronal activities, with special emphasis on signs of behaviorally induced modifications of neural interaction, possibly due to rapid modulations of discharge synchronization among the neurons. Our findings suggest that different functional groups of neurons may co-exist within each small volume of cortex, and that neurons may be dynamically recruited into such a group to fulfil a specific function.

Animals↗

PubMed1990

Oscillatory activity of single units in a somatosensory cortex of an awake monkey and their possible role in texture analysis.

Neuronal activity was extracellularly recorded in the cortex of an awake monkey (Macaca fascicularis). Single units displaying oscillatory firing patterns were found in the upper bank of the lateral sulcus in a region where most of the neurons responded to somatosensory stimuli. The spectral energies of the oscillating activity were distributed in a trimodal fashion--0-15, 15-50, and 80-250 Hz--with the most common frequencies around 30 Hz. The oscillatory activity was not affected by anesthesia, but it was often reduced by tactile stimulation or self-initiated movements. Analysis of the spike trains suggests that the majority of oscillatory activity was intrinsically generated by the neurons. A neural model of texture analysis is offered based on a corticothalamic phase-locked loop. The newly identified oscillators play a key role in this model. The relevance of the model to physiological, anatomical, and psychophysical data, as well as testable predictions, are discussed.

Action Potentials↗

PubMedDate not supplied

Hebbian-like functional plasticity in the auditory cortex of the behaving monkey.

In this study, the necessary conditions, including those related to behavior, for lasting modifications to occur in correlated activity ('functional plasticity') were examined in the behaving monkey. Previously, in-vitro studies of neuronal plasticity yielded important information about possible mechanisms of synaptic plasticity, but could not be used to test their functionality in the intact, behaving brain. In-vivo studies usually focused on analysis of the responsiveness of single cells, but did not examine interactions between pairs of neurons. In this study, we combined the two approaches. This was achieved by recording extracellularly and simultaneously the spike activity of several single cells in the auditory cortex of the behaving monkey. The efficacy of neuronal interactions was estimated by measuring the correlation between firing times of pairs of single neurons. Using acoustic stimuli, a version of cellular conditioning was applied when the monkey performed an auditory discrimination task and when it did not. We found that: (i) functional plasticity is a function of the change in correlation, and not of the correlation or covariance per se, and (ii) functional plasticity depends critically on behavior. During behavior, an increase in the correlation caused a short-lasting strengthening of the neuronal coupling efficacy, and a decrease caused a short-lasting weakening. These findings indicate that neuronal plasticity in the auditory cortex obeys a version of Hebb's associative rule under strong behavioral control, as predicted by Thorndike's "Law of Effect".

Acoustic Stimulation↗

PubMedDate not supplied

One whisker whisking: unit recording during conditioned whisking in rats.

Understanding of the functional neurobiology of the rodent whisker system would be advanced by neurobehavioral studies in awake, behaving animals that combine unit recording from structures at various levels of the system with quantitative characterization of the kinematics and temporal organization of whisking. Such studies require the solution of a number of methodological problems. These include: chronic recording procedures ensuring unit isolation, stability and maximum yield, monitoring and display of unit activity and whisker movements within the same (ms) timeframe and behavioral paradigms which bring whisking movement parameters under the control of the experimenter rather than the rat. Here we describe a head-fixed rodent preparation which makes possible chronic recording of unit activity in the awake, whisking rat, combined with real-time, high resolution monitoring of whisker and pad movements in two dimensions and under behavioral control. While the head-fixed "whisking" preparation has some inherent limitations, it may be used to address a number of important neurobehavioral problems. We suggest that it should contribute significantly to understanding the functional neurobiology of the whisker system.

Animals↗