Chapter 14. Electrical Activity of the Brain, Sleep–Wake States, & Circadian Rhythms
A healthy 23-year-old male medical student volunteered to have his EEG recorded as part of a class demonstration of cortical activity patterns. An electrode was placed over his occipital lobes and the activity was recorded initially while awake, sitting restfully with his eyes closed and then after opening his eyes and he is alert. The dominant EEG patterns observed during these two behaviors is expected to be
A. beta (18–30 Hz) rhythm and then alpha (8–13 Hz) rhythm, respectively.
B. delta (0.5–4 Hz) rhythm and then beta (18–30 Hz) rhythm, respectively.
C. alpha (8–13 Hz) and then beta (18–30 Hz) rhythm, respectively.
D. delta (0.5–4 Hz) rhythm and then fast, irregular low-voltage activity, respectively.
E. beta (18–30 Hz) rhythm and then fast, irregular low-voltage activity, respectively.
The correct answer is C. In healthy adults who are awake but at rest with their eyes closed, the most prominent component of the EEG is a fairly regular pattern of waves at a frequency of 8–13 Hz (alpha rhythm). When the eyes are opened and attention is focused on something, the alpha rhythm is replaced by fast irregular 13–30 Hz low-voltage activity (beta rhythm). This phenomenon is called alpha block and can be produced by any form of sensory stimulation or mental concentration, such as solving arithmetic problems. Another term for this phenomenon is the arousal or alerting response because it is correlated with the aroused, alert state. It has also been called desynchronization because it represents breaking up of the obviously synchronized neural activity necessary to produce regular waves. Option A can be ruled out as the description is the opposite of the behavioral-induced changes in the EEG pattern. A high-amplitude delta rhythm (0.5–4 Hz) dominates in stage 3 of NREM sleep (rules out options B and D). The appearance of these large amplitude rhythmic slow waves is indicative of marked synchronization of cortical activity during deep sleep; their appearance is also the reason that sometimes deep sleep is referred to as slow-wave sleep. Option E suggests that there was no behavioral-induced change in the EEG because beta rhythm is also described as fast, irregular low-voltage activity.
A 35-year-old man reported frequent episodes of daytime sleepiness over the course of the past year or so. His primary care physician recommended that he go to a sleep clinic to determine whether he has obstructive sleep apnea. An EEG recorded during an evening at the sleep clinic showed that NREM sleep accounted for over 30% of his total sleep time. What neurochemical changes in the brain trigger the transition from wakefulness ...