Tetrodes.
A tetrode is a four-wire bundle electrode that can be used to record
extracellularly from a cluster of adjacent cells in vivo. In
mammalian cortex, adjacent cells are known to be heavily
inter-connected and are thought to share physiological function. Thus
tetrodes may be used to explore local circuitry, concerted signalling
and population dynamics within a small volume.
The multiwire bundle makes the identification of multiple neurons in the extracellular record reliable and unambiguous. Research at Caltech has focused on finding a rigorous and quantifiable solution to the signal separation problem. Current work is now exploring areas in macaque parietal cortex with tetrodes.
This work is being done by
John Pezaris and
Maneesh Sahani in
Richard Andersen's laboratory.
Silicon Microprobes.
Other work at the Institute has focussed on the development of
micro-machined fork-shaped silicon probes, which support multiple
micro-electrodes on each of several tines of the fork (sixteen
electrodes total in current designs). Silicon neural probes are
expected to be one of the dominant experimental techniques in
neurophysiology in the future. Their inherent multichannel recording
ability compares to other extracellular techniques, while they provide
the added advantage of well defined electrode geometry.
These recording devices are being developed by
David Kewley in
Jim Bower's
group.
Living Neural Networks.
Researchers in
Jerry Pine's lab
use cultures of dissociated neurons from rat hippocampus to study the
morphological correlates of learning and memory. The neurons are
cultured for weeks or months at a time on 61-electrode arrays made of
the transparent conductor, indium-tin oxide (ITO), on a glass
substrate. By studying the basics of how electrical activity
influences neuronal morphology, and how these changes in morphology
then alter the networks' electrical properties, they will provide
useful parameters for computer models of neural networks. This will
allow the developmento of artificial learning systems that take
advantage of some of the clever adaptations that have evolved over the
ages in natural neural systems.
This work is done by
Steve M. Potter,
Devi Thota,
Michael P. Maher, and
Jerry Pine.
Olfactory Synchrony
Spike timing relationships across neural assemblies, such as synchrony
and oscillations, can best be explored by simultaneously recording
from multiple neurons. The roles of spike time phenomena in sensory
information processing can only be explored by doing so in intact
animals. Here a pair of neurons in the locust olfactory system are
shown to fire rhythmically and tightly locked to each other in
response to an apple odor. The red trace at the top shows field
potential oscillations, which indicate that many other neurons are
participating in the same synchronized, oscillatory assemblies.
This work is being done by Mike Wehr in the Laurent Lab.
