Unit quiz: Coordinating and modulating distributed circuits: rhythms, nuclei and the interfaces of the brain

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Question 1

A group reports that high gamma power (70 to 90 Hz) is coupled to the phase of hippocampal theta (6 to 8 Hz) during a memory task, and that coupling strength correlates with recall. Reviewers note that both theta power and high gamma power rose in the task, and that the raw power spectrum had a steeper 1/f slope in the task condition. What is the most defensible next step before the coupling is interpreted as a mechanism of information transfer?Recompute coupling after removing the aperiodic component of the spectrum and compare the observed coupling index against surrogate data that preserve power spectra but destroy phase relationships, because otherwise a change in the 1/f slope and in broadband power can generate apparent coupling without any change in phase organisation.Accept the coupling as evidence of information transfer, because a correlation with recall establishes that the coupled rhythm carries the memory code.

Question 2

In a two-armed bandit task, monkeys show a phasic locus coeruleus burst at the moment of a decision, and this burst is largest when the high-value option is clearly better than the alternative. Tonic firing rate is elevated instead when the value difference is small and the animal is sampling. A student concludes that noradrenaline signals reward value. Which reading is better supported?The burst tracks the value of the chosen option, and the tonic rise is a slower version of the same value signal, so noradrenaline is a value code.The pattern fits an adaptive-gain account in which phasic activity sharpens responding to the currently best option (exploitation) while raised tonic activity favours exploration, so the variable being signalled is the utility of responding to the current input rather than reward value itself.

Question 3

A 24-week randomised trial of a cholinesterase inhibitor in mild Alzheimer disease reports a 2.6-point advantage over placebo on a cognitive scale whose between-patient standard deviation is about 8 points, while the placebo group declines by 4 points over the same period. The sponsor describes the result as evidence that cholinergic loss drives the disease. Which conclusion is warranted?The trial shows a small symptomatic benefit, roughly a third of a standard deviation, in the context of continued decline; it does not show that cholinergic loss causes the disease, because a symptomatic effect on one transmitter system is compatible with many upstream causes.The trial confirms the cholinergic hypothesis, since a drug that raises cholinergic transmission produced measurable cognitive improvement.

Question 4

After a marathon, a runner has a serum S100B concentration above the laboratory reference range, and a popular article reports that endurance exercise makes the blood-brain barrier leaky. A separate study finds gadolinium enhancement in the choroid plexus and pituitary after contrast administration in healthy volunteers. Which response best characterises the evidence?Together the findings show that the barrier opens under physiological stress, which explains the cognitive fatigue reported after endurance events.Neither observation establishes generalised barrier failure: S100B is not specific to the brain and rises with muscle damage and haemolysis, and contrast uptake in circumventricular organs and the choroid plexus is expected because those sites lack an endothelial barrier.

Question 5

Healthy volunteers given low-dose endotoxin show a rise in plasma tumour necrosis factor at 90 minutes, peak self-reported nausea and fatigue at 3 hours, and a rise in plasma interleukin-6 that peaks at 4 hours. A commentary concludes that interleukin-6 causes sickness behaviour, because it is the cytokine that stays elevated longest. Which interpretation is best?The temporal order argues against interleukin-6 as the initiating signal; tumour necrosis factor rises first and the behavioural change follows it, while interleukin-6 is more consistent with a downstream amplifier whose peripheral concentration is a poor proxy for what the brain sees.Interleukin-6 is the best candidate because its elevation coincides with the period when participants feel worst and it remains high after the other cytokines fall.

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