Techniques to Study Brain Function

Researchers have developed multiple non-invasive techniques to study the complexities of the brain (Yuste & Church, 2014). Invasive techniques include microscopy, staining brain sections, histochemical staining, immunohistochemistry, common immunohistochemical markers, lectin stains, and cell culture (Watson et al., 2010). Non-invasive techniques include computed tomography (CT) scans, Functional magnetic resonance imaging (fMRIs), Positron Emission Tomography (PET), and Electroencephalography (EEG).

A CT scan is a collection of different X-ray measurements from a plethora of angles to create a three-dimensional image. These scans can show outlines of structures within the nervous system and can detect density variations. Using similar technology to MRIs, fMRIs detect differences in the flow of oxygenated blood levels in response to neural activity. During an fMRI, individuals are asked to perform a specific task (such as answering questions on a screen) which stimulates certain parts of the brain. In

performing this task, the brain requires more blood volume to transport glucose to the active areas. This increase in blood flow creates an image which can be used to examine functional anatomy of the brain. PET scans yield a three-dimensional map, produced as a result of scanning the brain with a gamma ray detector over relatively long periods of time; to obtain this map, individuals are intravenously administered radioactive

substances. EEGs represent electrical activity of the brain as recorded by placing multiple electrodes at different points on the scalp. EEGs can provide information about

amplitude, timing, spatial distribution, and frequency composition of electrical potentials (Watson et al., 2010). These noninvasive techniques have been extremely important for

understanding the maturation of emotional, cognitive, and social functions of the brain structures, and therefore are of considerable interest to this research from a wider perspective; EEGs in particular were employed in this research.

Typically, EEG data is recorded from metal electrodes coated with conductive paste that are applied to the scalp and held in place by a cap, adhesive, or suction

(Aminoff, 2012). The placement of the recording electrodes is based on the international 10-20 system, which describes four standard positions on the head: the nasion, inion, and right and left preauricular points (Figure 2.3). Odd number electrodes are located on the left side of the head while even numbers refer to the right side of the head.

Figure 2.3: International Electrode System (Li et al., 2017)

Note. AF= Anterior Frontal; CMS/DRI= Reference points; F=Frontal; FC= Frontal Central; O= Occipital Lobe; P= Parietal Lobe; T= Temporal Lobe

This system requires electrodes to be approximately 5-7cm apart. When neurons are activated, an electro-chemical current is produced; an EEG test measures this

electrical activity. These currents typically involve sodium, potassium, calcium, and chloride ions that are sent through channels in the neurons. Resulting electrical activity is measured by the scalp electrodes to produce graphic signatures based on specific energy characteristics, including frequency, amplitude, and distribution of electrical activity in resting state or external stimulation. Frequency is used to characterize electrical activity, which is often rhythmic. Frequency ranges of the EEG occur from 0.1-100 Hz. These frequencies are typically grouped into five brain wave classifications or rhythms: delta, theta, alpha, beta, and gamma (Teplan, 2002; Aminoff, 2012). Each different wave is associated with a certain brain function, all of which are discussed in the table below.

Table 2.3 Brain Wave Classification and Function (Teplan, 2002; Aminoff, 2012) Brain Wave

Classifications/Rhythm Hertz Brain Function

Delta 0.1-4 Sleep

Theta 4-7 Attentional Processing/ Working Memory

Alpha 7-13 Attentional Processing

Beta 14-30 Sensory Feedback

Gamma 32-100 Memory and Motor

Delta activity is mostly noted in infants or in deep sleep stages in older adults.

This activity is often associated with subjects with cortical plasticity and is prominent in cognitive processing during event-related studies such as P300. Delta waves are the primary contributor to P300, which is an indicator of cognitive processing (Malik &

Amin, 2017). Theta activity is noted in a drowsy state and is more common in children.

Age has an impact on theta activity, with older adults showing lower amplitude theta

activity than younger adults and children (Teplan, 2002). This activity is noted during attentional processing and working memory. Depression in adults can have an impact on theta activity (Malik & Amin, 2017). Alpha activity may occur between 8-13 Hz but is most often noted to occur between 9-11 Hz in adults (Teplan, 2002). Alpha waves are noted during wakefulness and in relaxed states in adults (Malik & Amin, 2017). When eyes are closed with no mental activity, these waves are observed primarily in the parietal region. Cognitive tasks and attentional processing attenuate these waves. The peak

frequency of these alpha waves is often an indicator of general intelligence (Grandy et al., 2013). Beta waves are observed in the frontal and central brain regions during anxious thinking, activeness, problem solving, and deep concentration (Gola et al., 2013). In individuals with high mental performance, these waves can be seen to increase in the occipital region during visual attention and spatial discrimination tasks. The activity of beta waves may be involved with cognitive processing and the motor system (Engel &

Fries, 2010). Gamma waves are observed during conscious perception; unlike the earlier waves, gamma waves are not widely studied but are reported to be involved in attention, long-term memory, and working memory (Jensen et al., 2007). Gamma activity is seen in psychiatric disorders such as schizophrenia, hallucinations, Alzheimer’s disease, and epilepsy (Herrmann & Demiralp, 2005).