Biomedical subjects

A Aertsen

Publications and source records attributed to A Aertsen.

41 records · Page 3Linked to original sources

PubMed1989

Synaptic plasticity in rat hippocampal slice cultures: local "Hebbian" conjunction of pre- and postsynaptic stimulation leads to distributed synaptic enhancement.

A central theme in neurobiology is the search for the mechanisms underlying learning and memory. Since the seminal work, first of Cajal and later of Hebb, the synapse is thought to be the basic "storing unit." Hebb proposed that information is stored by correlation: synapses between neurons, which are often coactive, are enhanced. Several recent findings suggest that such a mechanism is indeed operative in the central nervous system. Pairing of activity on presynaptic fibers with strong postsynaptic depolarization results in synaptic enhancement. While there is substantial evidence in favor of a postsynaptic locus for detection of the synchronous pre- and postsynaptic event and subsequent initiation of synaptic enhancement, the locus of this enhancement and its ensuing persistence is still disputed: both pre- and postsynaptic contributions have been suggested. In all previous studies, the enhancement was presumed to be specific to the synapses where synchronous pre- and postsynaptic stimulation was applied. We report here that two recording techniques--optical recording, using voltage-sensitive dyes, and double intracellular recordings--reveal that synaptic enhancement is not restricted to the stimulated cell. Although we paired single afferent volleys with intracellular stimulation confined to one postsynaptic cell, we found that strengthening also occurred on synapses between the stimulated presynaptic fibers and neighboring cells. This suggests that synaptic enhancement by the "paired-stimulation paradigm" is not local on the presynaptic axons and that, in fact, the synapses of many neighboring postsynaptic cells are enhanced.

Animals↗

PubMed1984

The neurochrome. An identity preserving representation of activity patterns from neural populations.

Recording of simultaneous but separated activity of neural populations overwhelms the experimenter with a large amount of information. A clearly structured display technique the "Neurochrome" is introduced, usable on-line and real-time. It shows neural activity patterns while preserving neural identity by employing a color code. The Neurochrome assists the experimenter in generating and verifying hypotheses about neural correlations and stimulus-event relations already during the experiment. In auditory research single neurons are characterized by their spectro-temporal sensitivity to auditory stimuli. A straightforward generalization of this concept, applicable to neural populations, is proposed leading to a global indication of a populations' activity to stimuli: the Multi-Unit Spectro-Temporal Sensitivity. This approach is inversely related to the Neurochrome, the latter however containing more information. The combination of both approaches seems quite powerful in the investigation of neural assemblies. The procedures are illustrated with examples of extracellular multiunit recordings from the auditory midbrain of the grassfrog (Rana temporaria L.).

Animals↗

PubMed1982

Statistical and dimensional analysis of the neural representation of the acoustic biotope of the frog.

The field of investigation is the neural representation of acoustic stimuli occurring in the natural environment of the frog. The point of departure is the description of a stimulus ensemble consisting of natural sounds: the acoustic biotope. A relation of statistical and dimensional structure of the acoustic biotope is indicated. The animal used in the neurophysiological experiments is the grass frog, Rana temporaria L.; microelectrode recordings are made in the auditory midbrain. A method is described to determine the existence of a relation between acoustic stimulus and neural events. The form of this relation has been investigated by first- and second-order stimulus-event correlation. While the first one does not give significant results, the second one leads to the spectrotemporal receptive field of the neuron for natural stimuli. Questions are formulated to estimate the value of this receptive field as a functional descriptor of the neuron. Finally, an outline is sketched for a synthetic construction of the bioacoustic space from neuroacoustic subspaces.

Acoustic Stimulation↗

PubMedDate not supplied

Propagation of cortical synfire activity: survival probability in single trials and stability in the mean.

The synfire hypothesis states that under appropriate conditions volleys of synchronized spikes (pulse packets) can propagate through the cortical network by traveling along chains of groups of cortical neurons. Here, we present results from network simulations, taking full account of the variability in pulse packet realizations. We repeatedly stimulated a synfire chain of model neurons and estimated activity (a) and temporal jitter (sigma) of the spike response for each neuron group in the chain in many trials. The survival probability of the activity was assessed for each point in (a, sigma)-space. The results confirm and extend our earlier predictions based on single neuron properties and a deterministic state-space analysis [Diesmann, M., Gewaltig, M.-O., & Aertsen, A. (1999). Stable propagation of synchronous spiking in cortical neural networks. Nature, 402, 529-533].

Action Potentials↗

PubMedDate not supplied

Accurate spike synchronization in cortex.

In view of the enormous capacity and complexity of mammalian brains it is evident that a detailed account of their anatomy and physiology alone cannot lead to a complete understanding of their function. Computer simulation and mathematical analysis of abstract, yet biologically realistic models for neurons and networks yield additional and useful information about the interplay of the underlying anatomical structures, the physiological processes operating on the neuronal substrate, and the resulting brain functions during the performance of behavioral tasks. We discuss some contributions of such experiment-guided theory to the issue of accurate spike synchronization.

Animals↗