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Measurement of Brain Activity Using Optical and Electrical Methods
(fNIRS). EEG is a method that measures brain activity using electrical brain
waves that propagate through the scalp (Sanei and Chambers 2007). Brain
waves can be measured using a small, portable device, so an EEG is suitable
for daily use. EEG signals are, however, susceptible to noise. Bioelectrical
signals originating from eye movements, facial muscular movement, and
external power sources such as electronic devices are common noise sources.
Furthermore, due to the fact that the electrical signals produced by the brain
have to travel through the skull and cerebrospinal fluid, it is difficult to
determine the origin of the signal.
fNIRS is a method that measures brain blood circulation information by
using near-infrared spectroscopy (NIRS). Differences in blood flow volume
reflect neural activities because higher neural activities require higher oxygen concentration and, therefore, higher blood circulation. By using noninvasive optical probes, it is possible to measure cortical neural activities around
a brain (Koizumi et al. 2003; Koizumi et al. 2005). Combining bioelectrical
activity data collected by brain electrodes with blood circulation data collected by optical probes, it is possible to measure brain activity and infer the
area of the brain that is active with a higher degree of precision than with the
methods currently available.
The objective of this chapter is to develop a hybrid sensor probe that can measure both optical and bioelectrical signals from the same spot simultaneously.
10.2 Methods to Measure Brain Activities
This section explains the methods used to measure brain activities.
10.2.1 Brain Wave Bioelectric Signal Measurement
EEG is the process of measuring electrical potential generated by several firing neurons simultaneously. These electrical signals propagate through the
brain, skull, cerebrospinal fluid, and scalp. A common method for measuring brain waves is measuring voltage by placing noninvasive low-impedance
electrodes on the patient’s scalp.
Some common passive brain waves include the following:
• Delta: 3 Hz and lower (deep sleep, when awake pathological)
• Theta: 3.5–7.5 Hz (creativity, falling asleep)
• Alpha: 8–13 Hz (relaxation, closed eyes)
• Beta: 14–30 Hz and higher (concentration, logical and analytical
thinking)
Measurement of Brain Activity Using Optical and Electrical Methods
(fNIRS). EEG is a method that measures brain activity using electrical brain
waves that propagate through the scalp (Sanei and Chambers 2007). Brain
waves can be measured using a small, portable device, so an EEG is suitable
for daily use. EEG signals are, however, susceptible to noise. Bioelectrical
signals originating from eye movements, facial muscular movement, and
external power sources such as electronic devices are common noise sources.
Furthermore, due to the fact that the electrical signals produced by the brain
have to travel through the skull and cerebrospinal fluid, it is difficult to
determine the origin of the signal.
fNIRS is a method that measures brain blood circulation information by
using near-infrared spectroscopy (NIRS). Differences in blood flow volume
reflect neural activities because higher neural activities require higher oxygen concentration and, therefore, higher blood circulation. By using noninvasive optical probes, it is possible to measure cortical neural activities around
a brain (Koizumi et al. 2003; Koizumi et al. 2005). Combining bioelectrical
activity data collected by brain electrodes with blood circulation data collected by optical probes, it is possible to measure brain activity and infer the
area of the brain that is active with a higher degree of precision than with the
methods currently available.
The objective of this chapter is to develop a hybrid sensor probe that can measure both optical and bioelectrical signals from the same spot simultaneously.
10.2 Methods to Measure Brain Activities
This section explains the methods used to measure brain activities.
10.2.1 Brain Wave Bioelectric Signal Measurement
EEG is the process of measuring electrical potential generated by several firing neurons simultaneously. These electrical signals propagate through the
brain, skull, cerebrospinal fluid, and scalp. A common method for measuring brain waves is measuring voltage by placing noninvasive low-impedance
electrodes on the patient’s scalp.
Some common passive brain waves include the following:
• Delta: 3 Hz and lower (deep sleep, when awake pathological)
• Theta: 3.5–7.5 Hz (creativity, falling asleep)
• Alpha: 8–13 Hz (relaxation, closed eyes)
• Beta: 14–30 Hz and higher (concentration, logical and analytical
thinking)