Neural Basis of Alertness and Cognitive Performance

The assignment discusses the neural basis of alertness and cognitive performance impairments during sleepiness, specifically exploring the effects of 24 hours of sleep deprivation on waking human regional brain activity. The study found that sleep deprivation led to a decrease in global CMRglu by 8%, with significant decreases in absolute regional CMRglu. Subjective and objective alertness declined, while mood remained constant. The results suggest that the deactivation of thalamic regions of the brain after sleep deprivation is associated with attention deficits in cognitive performances.

Notes for paper: Neural basis of alertness and cognitive performance impairments during
sleepiness. I. Effects of 24 h of sleep deprivation on waking human regional brain activity
(Thomas et al., 2000).
Aim(s):
 To test the hypothesis that negative effects of sleep deprivation on cognitive
performance decreases brain activity in the thalamus and sub-cortical regions.
Participant:
 n= 17 (mean age 24.7 +/- 2.8 years).
 Right handed males.
Study Design:
 7-8 hours of normal sleep volunteers.
 No nicotine abuse, low caffeine
 Normal range on mental state exams.
Protocol:
 Refrainment from intake of caffeine 3 days prior to study.
 First test- Wisconsin Card Sort Test, Fluency test (Benton and Thurstone's Word).
 Second test- Cognitive reaction time tasks.
 Multiple sleep latency tests.
 PET scanning.
 Follow definite sleeping patterns.
Measures:
 Polysomnography

 Cognitive tasks (Serial Addition and Subtraction)
 Neuroimage acquisition for measuring CMRglu.
 Self reports (Stanford Sleepiness Scale)
 Alertness test.
Results:
 Consistent sleep stage distribution prior to deprivation period (6 h and 36 minutes of
sleep).
 All subjects were awake during the FDG uptake period by polysomnography for 30
minutes.
 Voxel average showed a decrease in global CMRglu by 8% (~7.76%) after 24 hours
of sleep deprivation.
 Significant decrease in absolute regional CMRglu. It was 3+/- 7% greater than the
decrease in global CMRglu.
 No increase in absolute regional CMRglu.
 Subjective and objective alertness declined but mood remained constant.
 After SD, there was a reduction in cognitive performance during uptake of FDG.
 Efforts to perform Serial Addition and Subtraction task increased significantly after
SD.
 Time-on-task performance did not show any decrease when the segments were
compared.
Interpretation:
 The deactivation of thalamic regions of the brain after SD of 24 hours was consistent
with the role of thalamus in alertness and cerebral activation. It can also be associated
with the measured increase in subjective sleepiness and reduction in sleep latency.

 Focusing on the role of thalamus in attention and alertness, the decrease in its activity
can be associated to attention deficits in cognitive performances.
 Decreased regional brain activity during task performance indicates that neuronal
responsivity gets diminished after a certain period and reduces the task outcome.
 Data analysis of the study results will illustrate the brain regions that are most
sensitive to SD.
 The major neurobehavioral function of sleep is to sustain normal waking brain
activity in humans.