Exam 3 articles

Question 1

Describe the Synaptic Homeostasis Hypothesis.

Answer 1

• The Synaptic Homeostasis Hypothesis proposes that sleep actually weakens synapses
• Global synaptic weakening during sleep offsets global synaptic strengthening during wakefulness
• Synaptic weakening preserves the relative strength between synapses, promotes synaptic changes and prevents maladaptive metabolic costs linked to excessive synaptogenesis

Question 2

evidence for Synaptic Homeostasis Hypothesis

Answer 2

• Some molecular and electrophysiological studies have been consistent with SHY
• Some studies using adult rodents have shown that plasticity-related mRNAs are expressed at lower levels in the hippocampus or cortex after long periods of sleep versus long periods of wakefulness – possibly indicating reduction of synaptic efficacy during sleep

Question 3

evidence against Synaptic Homeostasis Hypothesis

Answer 3

• Difficult to find support for this hypothesis due to discrepancies in measures of plasticity
• Conflicting studies that have shown synapses might be stronger or more numerous following sleep
• When animals are trained in learning paradigms that trigger synaptic plasticity, sleep increases strength of synapses
• Changes in synaptic plasticity may be driven by circadian rhythms and don’t occur in one direction during the sleep phase

Question 4

Describe the State-Clock model presented by the authors, what evidence led the authors to favor this model?

Answer 4

• Biological clocks drive 24-hour, circuit-specific rhythms in synaptic plasticity
• During these rhythms, experience-dependent changes can be induced during wakefulness and consolidated during sleep
• Direction of changes during sleep is not fixed and depends on the type of experience that precedes sleep and the type of circuit
• Previous evidence has supported that biological clocks influence synaptic plasticity independently of vigilance state
• In insects and vertebrates, biological clocks produce rhythms in synaptic efficacy and number that appear timed to anticipate or match changes in activity

Question 5

What two factors controlled by circadian rhythms control alter global synaptic efficacy in the State-Clock model? How can this model be tested?

Answer 5

• Changes in brain temperature and hypothalamic-pituitary axis activity globally increase cortical synaptic efficacy during wakefulness, and globally decrease during sleep. This decrease during sleep results in global reductions in these processes
• Can be tested by measuring temperature changes and hormone release in relation to changes in number of synapses and synapse efficacy

Question 6

What are some features of medial temporal lobe amnesia?

Answer 6

• Medial temporal lobe amnesia is deficit in declarative memory
• Can be trained in hand-eye coordination skills, perceptual learning and visual and tactile maze learning
• When subjects weren’t told their memory would be tested, they showed preserved priming of single items
• Showed intact delay eye-blink classical conditioning
• Showed preserved learning abilities if there were many training sessions

Question 7

What are some arguments against using consciousness to define different memory systems?

Answer 7

• Memory systems can also be distinguished by number of learning trials, the cognitive complexity of tasks, and the nature of mental representations
• Hippocampus’ role in memory is not limited to conscious memory encoding or retrieval
• Acquiring and retrieving new associations requires intact medial temporal functioning and awareness that test items had been previously encountered as study items

Question 8

How does Henke propose we distinguish memory systems instead?

Answer 8

• Suggests that memory system divisions should be processing based with respect to three variables:
o Rapid versus slow encoding
o Associative versus single item encoding
o Flexible and compositional versus rigid and unitized representation

Question 9

What evidence supports Henke’s proposed distinction?

Answer 9

• Conscious awareness of encoding and retrieval is not a precondition for hippocampal processing
• Certain declarative and nondeclarative memory tasks have the same memory representations and that the crucial variable for the distinction between memory systems is whether or not the memory task requires the formation of a new association