Biomedical Engineering Reference
In-Depth Information
e
Figure 9.2:
Example of a biphasic electrogram.
H
H
Figure 9.3:
Electrograms from multineuron preparations.
The key to neural decoding is to assume that the electrodes do not move and that the action
potentials propagate at the same speeds down the axons. With these assumptions the firing of cell 1 will
always give the same pattern of deflections at electrodes 1 and 2. Likewise, the firing of cell 2 will always
generate the deflections in
φ
e
. The deflection in
φ
e
corresponding to a particular neuron will therefore
always have the same shape. In principle it is possible to use the extracellular shapes to sort or
bin
the
firings of individual neurons and therefore record the neural code from many neurons simultaneously.
9.2.2 Eavesdropping
An analogy to the recording and interpreting neural information is to imagine entering a room filled
with people speaking a foreign language that you do not understand. Upon entering the room you are far
from every individual conversation and so you hear mostly noise. In fact, all you may be able to infer is
how passionate the conversations are on the whole. If you move closer to any particular conversation you
may be able to gain more information on that particular group. Again, you do not speak their language,
