Biomedical subjects

Mathew E Diamond

Publications and source records attributed to Mathew E Diamond.

7 recordsLinked to original sources

PubMed2003

Effect of developmental sensory and motor deprivation on the functional organization of adult rat somatosensory cortex.

Most sensory systems are active, in the sense that the animal performs specific motor actions in order to collect information of interest-signals are not merely passively received. We, therefore, expect cortical development to depend not only correct sensory experience, but also on correct motor experience. In this study, we used the rat whisker system as a model to compare the importance of these factors. In one group of animals, we trimmed all whiskers starting from post-natal day 8 (P8). In a second group, we left the whiskers intact, but prevented "whisking" by sectioning the facial (VIIth cranial) nerve on P8. The first group had severely disrupted sensory experience but normal motor patterns ("whisker-cut" rats); the second group had normal sensory pathways within which temporal activity patterns were disrupted by motor impairment ("nerve-cut" rats). When they reached 3 months of age, we recorded multi-unit responses from the infragranular layers of primary somatosensory cortex in response to deflection of either single whiskers or pairs of whiskers in order to compare these two groups to a third group of rats that had normal sensory and motor experience. Cortical topographic organization was unaltered in whisker- and nerve-cut rats. Whisker-cut rats showed a smaller than normal difference between the response magnitudes for the principal and surrounding whiskers, as well as stronger than normal interactions between co-active whisker inputs. Responses in nerve-cut rats were nearly indistinguishable from those in normal animals. Thus, unexpectedly, neither pure sensory nor sensorimotor deprivation caused gross functional disruption of SI according to our measures. It appears that abnormal sensory experience leads to alterations in the fine-tuning of cortical properties, but cortex is unexpectedly resistant to the effects of abnormal sensory and sensorimotor experience.

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PubMed2003

Decoding neuronal population activity in rat somatosensory cortex: role of columnar organization.

The present study asks in what way the activity of a neuronal population responding to a sensory stimulus could be most efficiently decoded, or 'read off', by the target neurons. A simple solution to this problem has been proposed - pooling the activity of responding neurons. However, pooling can be inefficient if sensory information is encoded by the 'label' of each neuron firing a spike. We have tested the efficiency of pooling by quantifying the extent to which information about a sensory stimulus is diminished when the identity of the individual neurons is lost by pooling. Analyzing the response of small groups of neurons in rat barrel cortex to single-whisker deflection, we found that pooling neurons within the same column is efficient for representing stimulus position; it causes a loss of only 1% of the information about whether the principal whisker was stimulated, and a loss of 5-12% of the finer information about which of nine possible whiskers (the principal and its neighbors) was stimulated. Cross-column pooling led to larger information losses, in the range of 25-55%. Thus, to decode stimulus position from the discharge of barrel cortex populations, 'downstream' neurons could pool the activity arising from neurons of the same column, while maintaining the activity arising from neurons of separate columns at least partially segregated. Since such parcellation is present in some of the projections from barrel cortex, these findings suggest that columnar organization of barrel cortex serves to facilitate decoding of the location of the stimulated whisker.

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PubMed2002

Transient storage of a tactile memory trace in primary somatosensory cortex.

Working memory is known to involve prefrontal cortex and posterior regions of association cortex (e.g., the inferior temporal lobes). Here, we investigate the potential role of primary somatosensory cortex (SI) in a working memory task with tactile stimuli. Subjects were required to compare the frequencies of two vibrations separated by a retention interval of 1500 msec. Their performance was significantly disrupted when we delivered a pulse of transcranial magnetic stimulation (TMS) to the contralateral SI early (300 or 600 msec) in the retention interval. TMS did not affect tactile working memory if delivered to contralateral SI late in the retention interval (at 900 or 1200 msec), nor did TMS affect performance if delivered to the ipsilateral SI at any time point. Primary sensory cortex thus seems to act not only as a center for on-line sensory processing but also as a transient storage site for information that contributes to working memory.

Adult↗

PubMed2002

Population coding in somatosensory cortex.

Computational analyses have begun to elucidate which components of somatosensory cortical population activity may encode basic stimulus features. Recent results from rat barrel cortex suggest that the essence of this code is not synergistic spike patterns, but rather the precise timing of single neuron's first post-stimulus spikes. This may form the basis for a fast, robust population code.

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PubMed2002

Somatosensory cortical neuronal population activity across states of anaesthesia.

Experiments were carried out to learn about changes in sensory cortical processing associated with different levels of anaesthesia. Traditionally this question has been addressed by studying single neurons. Because state changes are likely to influence the relationships between neurons, the present experiments were undertaken to investigate the spatial and temporal firing patterns distributed across cortex. Using 5 x 5 or 10 x 10 microelectrode arrays, spontaneous and stimulus-evoked activity of multineuron clusters was recorded from rat somatosensory 'barrel' cortex (the whisker representation) during a light surgical stage of urethane anaesthesia, and after two supplemental doses of urethane which led to intermediate and deep levels of anaesthesia. At all depths of anaesthesia, spontaneously occurring action potentials at a single electrode tended to be clustered into 'bursts.' With increasing anaesthetic depth, bursts became more prominent and rhythmic, and increasingly synchronized between cortical barrel-columns. Burst frequency decreased and fewer spikes occurred outside bursts, leading to a decrease in the overall spontaneous firing rate. The cortical territory engaged by individual whiskers contracted with increasing depth of anaesthesia, leading to the spatial segregation of whisker representations. At all stages of anaesthesia, whisker stimulation produced the maximal cortical response when delivered close to burst onset. These observations show that ongoing spontaneous activity modulates sensory response properties and makes peripheral tactile information accessible to a cortical territory whose size is determined by the phase of burst cycle. The possible significance of the cyclic cortical responsiveness encountered during urethane anaesthesia to cortical processing in awake rats is considered.

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PubMedDate not supplied

The role of individual spikes and spike patterns in population coding of stimulus location in rat somatosensory cortex.

This report addresses the nature of population coding in sensory cortex by applying information theoretic analysis to data recorded simultaneously from neuron pairs located in primary somatosensory cortex of anaesthetised rats. We studied how cortical spike trains code for the location of a whisker stimulus on the rat's snout. We found that substantially more information was conveyed by 10 ms precision spike timing compared with that conveyed by the number of spikes counted over a 40 ms response interval. Most of this information was accounted for by the timing of individual spikes. In particular, it was the first post-stimulus spikes that were crucial. Spike patterns within individual cells played a smaller role; spike patterns across cells were negligible. This pattern of results was robust both to the exact nature of the stimulus set and to the precision at which spikes were binned.

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PubMedDate not supplied

Redundancy and synergy arising from pairwise correlations in neuronal ensembles.

Multielectrode arrays allow recording of the activity of many single neurons, from which correlations can be calculated. The functional roles of correlations can be revealed by measures of the information conveyed by neuronal activity; a simple formula has been shown to discriminate the information transmitted by individual spikes from the positive or negative contributions due to correlations (Panzeri et al., 1999). Here, this analysis, previously applied to recordings from small ensembles, is developed further by considering a model of a large ensemble, in which correlations among the signal and noise components of neuronal firing are small in absolute value and entirely random in origin. Even such small random correlations are shown to lead to large possible synergy or redundancy, whenever the time window for extracting information from neuronal firing extends to the order of the mean interspike interval. In addition, a sample of recordings from rat barrel cortex illustrates the mean time window at which such "corrections" dominate when correlations are, as often in the real brain, neither random nor small. The presence of this kind of correlations for a large ensemble of cells restricts further the time of validity of the expansion.

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