Advances in Neural Signal Processing
2
brain. In order to investigate how the motor-related information is generated, and
what kind of patterns could be found in certain areas during a specific action, many
engineering methodologies are applied.
In the human brain, neurons communicate with each other through connections
known as synapses. Synapses can be electrical or chemical, and the excitatory or
inhibitory nature of synapses contributes to information transmission—the influx
and outflux of sodium and potassium causing the membrane potential to rise and
fall rapidly. The rapid changes of membrane potentials are called spikes, which
can be recorded by intercellular or extracellular recordings. Valuable information
can be discovered from the rate of spikes, namely, the firing rate. The deep brain
implanted electrodes allow the recording from individual neurons and can present
significant results in awake animals but not in humans. Multielectrode arrays can
record the voltage oscillations from multiple neurons. Simultaneously recording
from a large population of local neurons increases spatial resolution benefits to
the extraction of complex information in contrast with single-unit recordings.
The aforementioned invasive recording technologies provide considerably less
vulnerability to artifacts and relevantly higher resolution and larger amplitudes
(voltages), and thereby the performance relies much more on the technologies
of electrodes. However, there are several limitations of these invasive recording
technologies including restricted to clinical environments and the risks of surgery
and implantations.
As an alternative to the constrained invasive technologies, several noninvasive
recording technologies such as electroencephalography and magnetoencephalography have been used in human studies. Advanced computational algorithms
promise to promote signal processing and signal filtering; thus, more and more
noninvasive recording technologies are being considered in human studies. Some
techniques record neuronal potentials from the scalp, and such recordings capture
the population activity of thousands of neurons depending on the level of recording. Multiple layers restrict information transmission from the cerebral cortex to
the scalp leading to lower amplitudes of the signal and lower spatial resolution.
Additionally, the electrodes are sensitive to the surrounding interferences like eye
movements, facial movements, chewing, swallowing, etc. Therefore, it is necessary
to apply robust and efficient signal processing technologies to amplify the neural
activity and filter out the ambient and transducer noise, thus improving the signalto-noise ratio.
Under noninvasive technologies, there are imaging methods that focus on the
metabolic activity in the brain rather than the activity of neurons or the population
of neurons. When performing a specific task, the activation of the brain neurons
is enhanced and thereby more oxygen is required and absorbed from surrounded
blood vessels. An increased inflow and higher oxygenated level can be detected.
This hemodynamic response is comparatively slow that it reaches the peak in a few
seconds and takes a longer time to fall back to the original level. Therefore, this kind
of recording technology provides good spatial resolution but very poor temporal
resolution.
In addition to neural recording technologies, there are also neural stimulation
technologies that are used in clinical treatments (cochlear implants and deep
brain stimulators) and emerging neuroprosthetics. This involves giving electrical
or magnetic stimulation to a particular region of the brain to mimic sensorimotor feedback. Most recording electrodes can also be used for stimulations. Brain
stimulations have proven effective in clinical treatments. These methodologies
also involve the use of signal processing methodologies in determining ideal
stimulation patterns. Table 1 summarizes neural recording and stimulation
technologies.
2
brain. In order to investigate how the motor-related information is generated, and
what kind of patterns could be found in certain areas during a specific action, many
engineering methodologies are applied.
In the human brain, neurons communicate with each other through connections
known as synapses. Synapses can be electrical or chemical, and the excitatory or
inhibitory nature of synapses contributes to information transmission—the influx
and outflux of sodium and potassium causing the membrane potential to rise and
fall rapidly. The rapid changes of membrane potentials are called spikes, which
can be recorded by intercellular or extracellular recordings. Valuable information
can be discovered from the rate of spikes, namely, the firing rate. The deep brain
implanted electrodes allow the recording from individual neurons and can present
significant results in awake animals but not in humans. Multielectrode arrays can
record the voltage oscillations from multiple neurons. Simultaneously recording
from a large population of local neurons increases spatial resolution benefits to
the extraction of complex information in contrast with single-unit recordings.
The aforementioned invasive recording technologies provide considerably less
vulnerability to artifacts and relevantly higher resolution and larger amplitudes
(voltages), and thereby the performance relies much more on the technologies
of electrodes. However, there are several limitations of these invasive recording
technologies including restricted to clinical environments and the risks of surgery
and implantations.
As an alternative to the constrained invasive technologies, several noninvasive
recording technologies such as electroencephalography and magnetoencephalography have been used in human studies. Advanced computational algorithms
promise to promote signal processing and signal filtering; thus, more and more
noninvasive recording technologies are being considered in human studies. Some
techniques record neuronal potentials from the scalp, and such recordings capture
the population activity of thousands of neurons depending on the level of recording. Multiple layers restrict information transmission from the cerebral cortex to
the scalp leading to lower amplitudes of the signal and lower spatial resolution.
Additionally, the electrodes are sensitive to the surrounding interferences like eye
movements, facial movements, chewing, swallowing, etc. Therefore, it is necessary
to apply robust and efficient signal processing technologies to amplify the neural
activity and filter out the ambient and transducer noise, thus improving the signalto-noise ratio.
Under noninvasive technologies, there are imaging methods that focus on the
metabolic activity in the brain rather than the activity of neurons or the population
of neurons. When performing a specific task, the activation of the brain neurons
is enhanced and thereby more oxygen is required and absorbed from surrounded
blood vessels. An increased inflow and higher oxygenated level can be detected.
This hemodynamic response is comparatively slow that it reaches the peak in a few
seconds and takes a longer time to fall back to the original level. Therefore, this kind
of recording technology provides good spatial resolution but very poor temporal
resolution.
In addition to neural recording technologies, there are also neural stimulation
technologies that are used in clinical treatments (cochlear implants and deep
brain stimulators) and emerging neuroprosthetics. This involves giving electrical
or magnetic stimulation to a particular region of the brain to mimic sensorimotor feedback. Most recording electrodes can also be used for stimulations. Brain
stimulations have proven effective in clinical treatments. These methodologies
also involve the use of signal processing methodologies in determining ideal
stimulation patterns. Table 1 summarizes neural recording and stimulation
technologies.