Biomedical Engineering Reference
In-Depth Information
Postsynaptic
Membrane
Potential
Action Potential
0 -
Firing Threshold
EPSP
IPSP
Time
FIgURE 2.2:
The time course of postsynaptic potentials. EPSP, excitatory postsynaptic potential; IPSP,
inhibitory postsynaptic potential.
arrays are placed in layer V of the neocortex, close to the pyramidal/stellate cell bodies to measure
their action potentials. The generation of an action potential, or spike, is considered to be the basic
unit of communication among neurons. Measurement of the action potential resulting from ionic
current exchanges across the membranes of neurons has been sought after for many years through
the use of microelectrode recording technology [
16
].
An example of a microelectrode recording from a single neuron collected extracellularly near
the cell body is shown in Figure
2.3
a. Typical cellular potentials have magnitudes ranging from
tens of microvolts to tens of millivolts, and time durations of a millisecond. The action potentials
in Figure
2.3
a are of the same amplitude and have the same shape, which indicates they are from
the same neuron. The amplitude and shape of the measured action potential is affected by the elec-
trode-neuron distance and orientation [
17
]. The ability to automatically discriminate the activity
of individual neurons in a given electrode recording has been a formidable computational challenge
with respect to the experimental conditional and subjective observations traditionally used to sort
action potentials from each other [
18
]. Accurate spike detection and sorting is a critical step for
high-performance BMIs because its role is to identify from the background noise the neuromodula-
tion related to movement intent and execution. To date, accurate and automated spike detection and
sorting remains an ongoing research topic [
18-21
]. One of the complexities of analyzing neuronal
activity is the fact that neurons are active in assemblies surrounding the electrode. In Figure
2.3
b,
