With colleagues including Miles A. Whittington and Eberhard Buhl (Leeds, U.K.) and Andrea Bibbig, I have been working on three general problems.

a) The organization of transient gamma (30-70 Hz) -> beta (10 - 30 Hz) oscillations in hippocampal slices;
b) The generation of very fast (>70 Hz) oscillations in networks of electrically coupled neurons;
c) Population phenomena that result in networks in which both chemical synapses and gap junctions work together.

Gamma/beta oscillations occur in vivo, including in humans, in response to sensory stimulation, and are thought to be important in linking together features of spatially distributed sensory inputs. An experimental model of this phenomena exists in slices, in that brief tetanic stimulation can evoke - after a variable latent period of about 100 ms - gamma, followed by a train of beta, provided the stimulus is strong enough. It is of particular interest that the experimental oscillations can - like the in vivo ones - synchronize tightly over distances of several mm, despite the presence of axon conduction delays. Electrophysiology and computer modeling have worked together in uncovering many of the cellular mechanisms, and in providing an explanation for the means by which long-range synchrony can occur. The latter involves the special firing properties of interneurons. Work is in progress now to study how synaptic plasticity influences the shaping of these oscillations, and whether beta could be involved in memory.

Very fast oscillations occur in vivo, and also in hippocampal slices, even when chemical synapses are blocked. In the latter case, gap junctions are known to be involved. The shape of the coupling potentials suggests that the site of coupling is novel: Between axons. Dietmar Schmitz (UCSF) and colleagues in Germany have provided experimental evidence that axonal gap junctions do indeed exist between principal neurons in the hippocampus (Neuron, Sept. 2001). In the meantime, computer simulations have shown that axonal coupling can indeed lead to very fast oscillations, by a novel mechanism.

Simulations also indicate that gap junctions and chemical synapses can cooperate to generate a variety of population phenomena, including carbachol-induced gamma oscillations, and in vivo 200 Hz ripples. Work is in progress to extend this analysis to other phenomena, including oscillations evoked by hypertonic [K] solutions, 4AP-induced giant IPSPs, and seizure -like events evoked in the slice in the presence of gap-junction-opening drugs.

Figure 1. EEG data from a subdural grid in a child with focal cortical dysplasia, showing a very fast oscillation (about 100 Hz) in selected channels (e.g. channels 13, 21 and 22, all of which are near to each other) near the beginning of the trace. The very fast activity leads then into an electrographic (and clinical) seizure. From R. D. Traub et al. (2001)., Epilepsia 42, 153-170.

Figure 2. Simulation of low amplitude very fast oscillatory activity, leading into a population burst, in a network of pyramidal neurons, interconnected by axonal gap junctions. From R. D. Traub et al. (1999)., Neuroscience 92, 407-426.

Selected Publications

Traub, R. D., and Wong, R. K. S. (1982). Cellular mechanism of neuronal synchronization in epilepsy. Science 216, 745-747.

Traub, R. D., Whittington, M. A., Stanford, I. M., and Jefferys, J. G. R. (1996). A mechanism for generation of long-range synchronous fast oscillations in the cortex. Nature 383, 621-624.

Traub, R. D., Schmitz, D., Jefferys, J. G. R., and Draguhn, A. (1999). High-frequency population oscillations are predicted to occur in hippocampal pyramidal neuronal networks interconnected by axoaxonal gap junctions. Neuroscience 92, 407-426.

Traub, R. D., and Bibbig, A. (2000). A model of high-frequency ripples in the hippocampus, based on synaptic coupling plus axon-axon gap junctions between pyramidal neurons. J. Neurosci. 20, 2086-2093.

Schmitz, D., Schuchmann, S., Fisahn, A., Draguhn, A., Buhl, E. H., Petrasch-Parwez, E., Dermietzel, R., Heinemann, U., and Traub, R. D. (2001). Axo-axonal coupling: A novel mechanism for ultrafast neuronal communication. Neuron 31, 831-840.

List of Publications (Pub Med)

Personnel

Andrea Bibbig, Ph.D., Research Assistant Professor

Service Functions

Action Editor or Editorial Board Member for Journal of Computational Neuroscience, Neuronal Computation, and Journal of Neuroscience Methods.
Reviewer for various journals.