Passage 9
Sedentary behavior (defined as an energy expenditure of <1.5 METs while lying,
sitting, or reclining, while awake can be detrimental for cognitive performance,
whereas acute physical activity breaks may elicit positive effects. One of the main
underlying mechanisms driving the acute physical activity-induced improvements
on cognitive performance is assumed to be changes in cerebral blood flow driven by
neural activation. Previous research findings have demonstrated that a single bout of
physical activity (about 10–20 min) can increase such task-related cerebral blood
flow, with coinciding improvements in prefrontal cortex-dependent cognitive tasks.
However, decreases in task-related cerebral blood flow after an exercise bout with
concomitant enhancement in cognitive performance has also been observed.
In this randomized crossover study, the effects of frequent, short physical activity
breaks during prolonged sitting on cognitive task-related activation of the prefrontal
cortex were investigated. The effects on working memory, psychological factors,
and blood glucose were also examined, and whether arterial stiffness moderated
prefrontal cortex activation. Thirteen subjects (mean age 50.5 years; eight men)
underwent three 3-h sitting conditions, interrupted every 30-min by a different 3-min
break on separate, randomized-ordered days: seated social interactions (SOCIAL),
walking (WALK), or simple resistance activities (SRA). Arterial stiffness was assessed
at baseline. Before and after each 3-h condition, psychological factors (stress, mood,
sleepiness, and alertness) were assessed through questionnaires and functional nearinfrared spectroscopy (fNIRS) was used to measure changes in prefrontal oxygenated
hemoglobin (Oxy-Hb), indicative of cortical activation, while performing working
memory tasks [1- (baseline), 2-, and 3-back]. Blood glucose levels were continuously
measured throughout the conditions.
Results revealed no significant changes in Oxy-Hb during the 2-back compared
with the 1-back test in any condition, and no time-by-condition interactions. During
the 3-back test, there was a significant decrease in Oxy-Hb compared with the
1-back after the WALK condition in the right prefrontal cortex, but there were no
time-by-condition interactions, although 3-back reaction time improved only in the
WALK condition. Mood and alertness improved after the WALK condition, which was
significantly different from the SOCIAL condition. Arterial stiffness moderated the
effects, such that changes in Oxy-Hb were significantly different between WALK and
SOCIAL conditions only among those with low arterial stiffness. Blood glucose during
the interventions did not differ between conditions. Thus, breaking up prolonged
sitting with frequent, short physical activity breaks may reduce right prefrontal
cortex activation, with improvements in some aspects of working memory, mood,
and alertness.
Interrupting prolonged sitting, with frequent, short walking breaks decreased taskrelated right prefrontal cortex activation as measured by Oxy-Hb during a high load
working memory task. Still, frequent, short walking breaks also enhanced working
memory performance, suggesting that physical activity breaks during prolonged
sitting may help preserve or even improve neural efficiency. Of further importance,
alertness and positive mood were enhanced by frequent, short walking breaks
compared with prolonged sitting. While more experimental scrutiny is needed to
clarify the physiological mechanisms underlying such improved neural efficiency,
frequent, short walking breaks may be recommended in middle-aged adults to
support psychological well-being during extended periods of sitting and cognitive
performance on mentally demanding tasks.
Frequent, Short Physical Activity Breaks Reduce Prefrontal Cortex Activation but
Preserve Working Memory in Middle-Aged Adults: ABBaH Study. Adapted from
Heiland et al. (2021).
Which of the following structures in the diagram above is responsible for
speeding action potentials along the axon?
A) Structure A
B) Structure C
C) Structure D
D) Structure E
Correct answer is D
The diagram shown depicts the various parts of the neuron, which is the functional
unit of the brain. Neurons are the cells primarily responsible for transmitting
information within and around the brain, and are created and destroyed as various
neural pathways are removed, strengthened, or created.
In the diagram above,
Structure A corresponds to the dendrites
Structure B corresponds to the cell body, where the nucleus of the neuron is housed.
Structure C corresponds to the axon hillock
Structure D corresponds to the myelin sheath
Structure E corresponds to the nodes of Ranvier
Structure F corresponds to the axon terminals
Of the structures listed, the myelin sheath (Structure D) is responsible for
speeding action potentials along the axon from the axon hillock (Structure C)
to the axon terminals (Structure F), which then connect to other neurons and
provide information that can then be further transmitted. Composed of either
oligodendrocytes (for the central nervous system, or CNS) or Schwann cells (for the
peripheral nervous system, or PNS), the myelin sheath (Structure D) is a structure
composed of specialized lipids, and serves as a type of insulation material that
prevents electrical potential from being lost as propagation of the action potential
occurs. The myelin sheath is discontinuous, and between sections of myelin sheath
are the nodes of Ranvier (Structure E), which help speed action potentials along the
axon. For this reason, Answer D is correct and Answers A, B, and C are incorrect.
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