Questions: Neural Oscillations and Cognitive Dynamics

Question 1

A researcher records EEG from a participant who is focusing full attention on an auditory task while ignoring visual input. What would you expect to happen to alpha power in the visual cortex?

• A. Alpha power decreases, because the visual cortex is inactive and no longer generating oscillations
• B. Alpha power increases, because elevated alpha reflects active suppression of the visual cortex while attention is directed elsewhere
• C. Gamma power increases in visual cortex, because high-frequency oscillations fill the void left by inattention
• D. Alpha power stays the same, because alpha reflects baseline resting activity

Answer: (B)

Alpha power increasing in visual cortex is the correct prediction — and the counterintuitive insight of this topic. Alpha does not reflect mere absence of activity; it is an active inhibitory mechanism. When attention is directed away from vision, the visual cortex is actively suppressed, and alpha power rises as a result. The contralateral hemisphere (relative to attended space) shows reduced alpha, while the ipsilateral hemisphere shows increased alpha. This is attentional gating: the brain uses alpha to gate out irrelevant sensory channels, not merely to idle.

Question 2

What does it mean that gamma oscillations are 'nested within' theta oscillations during working memory tasks?

• A. Gamma and theta oscillations have the same frequency but different amplitudes during memory tasks
• B. Gamma bursts occur preferentially at specific phases of the theta cycle — the amplitude of gamma is modulated by the phase of theta
• C. Theta oscillations are generated first in the hippocampus and then trigger gamma oscillations in the cortex with a time delay
• D. Gamma and theta are two independent oscillations that both increase in power during memory tasks

Answer: (B)

Phase-amplitude coupling means the amplitude (strength) of gamma oscillations is systematically higher at certain phases of the theta cycle and lower at others — not that they merely co-occur. During working memory tasks, gamma bursts tend to cluster on the peak of each theta cycle. The proposed functional interpretation is that each theta cycle acts as a 'slot' holding one item in working memory, and the gamma activity within that slot encodes the item's content. This hierarchical nesting is the proposed mechanism for serializing multiple items in memory across theta cycles.

Question 3

Higher oscillatory frequency in a brain region reliably indicates greater cognitive processing or neural excitability in that region.

• T. True
• F. False

Answer: False

This is the central misconception this topic addresses. Alpha oscillations (8–13 Hz) are a clear counterexample: increased alpha power in a region corresponds to *reduced* excitability and active suppression of processing — the opposite of what the naive 'higher frequency = more activity' rule would predict. The relationship between frequency and function is not monotonic. Each frequency band has its own functional signature (delta: sleep consolidation; theta: hippocampal memory; alpha: attentional suppression; beta: motor maintenance; gamma: local feature binding) that must be understood in its own right.

Question 4

Alpha oscillations can actively suppress neural processing in a brain region, not just reflect that the region happens to be uninvolved in the current task.

• T. True
• F. False

Answer: True

Correct — this is one of the most important findings from attention neuroscience. Experimental work shows that alpha increases precede the suppression of responses to stimuli in the corresponding sensory area. Causal manipulations (e.g., transcranial magnetic stimulation timed to specific alpha phases) can alter perception in predictable ways. Alpha is an active inhibitory mechanism, likely operating through the pulsed suppression of neural excitability at the alpha rhythm rate — effectively gating out sensory input that is not behaviorally relevant.

Question 5

Why should a researcher be cautious about concluding that increased alpha power in a brain region means more cognitive processing is occurring there?

Model answer: Increased alpha power is associated with *reduced* excitability and active suppression of processing, not increased activity. Alpha increases when a region is being inhibited — for example, in the visual cortex when attention is directed elsewhere, or in the ipsilateral hemisphere relative to the attended visual field. Interpreting alpha power increases as evidence of greater processing reverses the relationship and would lead to incorrect conclusions about which brain regions are involved in a task.

The counterintuitive direction of the alpha-activity relationship is one of the most important empirical findings in cognitive neuroscience. It was established by showing that alpha power systematically increases in task-irrelevant regions and decreases in task-relevant regions during attentional tasks. The mechanism appears to be pulsed suppression of neural excitability: neurons in a high-alpha state receive inhibitory input synchronized to the alpha rhythm, reducing their firing rate and their influence on downstream areas.