Abnormal Psychology - William J. Ray

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2.9 on page 49 shows different levels of firing. Understanding the nature of spikes and how they relate to information in the brain has been an important question since the beginning of the twentieth century when they were first recorded (Rieke, Warland, van Steveninck, & Bialek, 1999).

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      Figure 2.8 The Role of Neurotransmitters in Synaptic Processes

      Source: Magistretti, P. J. (2009). Low-cost travel in neurons. Neuroscience Science, 325(5946), 1349–1351. doi:10.1126/science.118102. Retrieved from http://www.sciencemag.org/content/325/5946/1349.short. Reprinted with permission from American Association for the Advancement of Science (AAAS).

      Let us now move from the consideration of neurons and neurotransmission to an overview of some of the specific neuroscience techniques that are used to understand psychopathological processes. Following an examination of these neuroscience techniques, I will move to a discussion of the networks of the brain.

      Concept Check

       What are the four major lobes of the brain, and what is the primary role of each?

       “The brain’s function involves one basic element, the neuron.” What are the different parts that form the structure of the neuron, and what roles do they play?

       How does the neuron pass information on to other neurons, and how is that information encoded?

       Table 2.1 Table 2

      How Do We Observe the Brain at Work?

      With 86 billion neurons and 50 to 200 trillion connections between neurons in the human brain, understanding these connections on a neuronal level would be an impossible task. However, scientists have been able to use the manner in which neurons work as a window into their function. A variety of techniques for observing activity in the brain have been developed.

      Currently, the major types of brain imaging techniques are electroencephalography (EEG), magnetoencephalography (MEG), positron emission tomography (PET), and functional magnetic resonance imaging (fMRI). EEG is a technique for recording electrical activity from the scalp related to cortical activity. MEG measures the small magnetic field gradients exiting and entering the surface of the head that are produced when neurons are active. PET is a measure related to blood flow in the brain, which reflects cognitive processing. fMRI is based on the fact that blood flow increases in active areas of the cortex. It is also possible to use the magnetic resonance imaging (MRI) magnet to measure cortical connections in the brain, which is referred to as diffusion tensor imaging (DTI). Let’s take a look at each of these techniques, and consider the strengths and weaknesses of each type.

Figure 20

      Figure 2.9 Spike Trains Produced by Different Levels of Firing of Neurons

      Source: Spencer, W. (2011). The Physiology of Supraspinal Neurons in Mammals. Supplement 1: Handbook of Physiology, The Nervous System, Cellular Biology of Neurons, pp. 969–1021. First published in print, 1977.

      Electroencephalography

      Electroencephalography (EEG) is a technique for recording electrical activity from the scalp related to cortical activity. It reflects the electrical activity of the brain at the level of the synapse (Nunez & Srinivasan, 2006). It records the product of the changing excitatory and inhibitory currents. Action potentials contribute very little to the EEG. However, since changes at the synapse do influence the production of action potentials, there is an association of EEG with spike trains (Whittingstall & Logothetis, 2009).

Image 63

      EEG measures the electrical activity of the brain as found on the scalp.

      Science Photo Library/Brand X Pictures/Getty Images

      electroencephalography (EEG): a technique for recording electrical activity from the scalp, which measures the electrical activity of the brain at the level of the synapse

      The EEG was first demonstrated in humans by Hans Berger in 1924, and results were published 5 years later (Berger, 1929/1969). Since the neurons of the brain and their connections are constantly active, EEG can be measured during both waking hours and sleep. In fact, EEG serves as an objective measure of depth of sleep (see Figure 2.10).

      EEG can be measured with only two electrodes or as a high-density array of more than 200 electrodes. EEG activity has been used to infer brain processing. The actual measure of EEG is the difference between the signals at any two electrodes. Traditionally, the second or reference electrode was placed at a location not considered to produce electrical signals, for example, the ear lobe. Today, a common practice is to average the signals in all of the electrodes available and compare that with each specific electrode.

Image 64

      An EEG “cap” that holds the electrodes is placed over the subject’s head.

      Don Tucker

      Some aspects of the EEG signal may appear almost random, while other fluctuations appear periodic. Using signal processing techniques, it is possible to determine the major frequency and amplitude seen in the signal. Amplitude refers to how large the signal is, and frequency refers to how fast the signal cycles, measured in cycles per second, or Hertz (Hz). Over the years, researchers have noticed that specific patterns of EEG activity were associated with a variety of psychological states (see Figure 2.11). When an individual is relaxed with his or her eyes closed, high-amplitude regular activity is seen in the EEG at a frequency of 8 to 12 Hz. Alpha activity in the 8 to 12 Hz range was the first pattern of EEG activity Hans Berger noted. If the person begins to perform some mental activity such as mental arithmetic, lower-amplitude EEG is seen at a higher frequency, above 20 Hz, and is referred to as beta activity.

      EEG oscillations are one way in which information is transferred in the brain (Knyazev, 2007). For example, theta oscillations are associated with memory performance (Liebe, Hoerzer, Logothetis, & Rainer, 2012). Theta is also involved in coordinating emotional information between the limbic areas and the frontal areas of the brain. Delta oscillations are seen in sleep and motivational processes such as drug use. Drugs such as cocaine produce changes in a number of EEG frequency bands. Alpha oscillations, on the other hand, are involved in inhibiting the activity of various brain areas.

      In recent years, researchers have become interested in the processing of a percept (Singer, 2009; Singer & Gray, 1995; Tallon-Baudry & Bertrand, 1999). For example, when one sees a black and white spotted Dalmatian dog against a black and white background, there is usually a subjective experience of having the image “pop out.” Associated with this perception is a burst of EEG gamma activity. Figure 2.12 compares the amount of EEG gamma activity in those individuals trained to see the Dalmatian as compared with those who were not trained.

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      Figure 2.10 Electroencephalogram as an Objective Measure of Sleep Stages

      Source: P. Hauri, Current Concepts: The Sleep Disorders, 1982, Kalamazoo, MI: Upjohn.

Figure 22

      Figure 2.11 Depiction of Specific Patterns of Electroencephalography Activity

      Source: Hugo Gambo (2005), Wikipedia.

      event-related potentials (ERPs):

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