Changes in measures of consciousness during anaesthesia of one hemisphere (Wada test)
Published in NeuroImage, 2021
The Wada test provides a rare naturalistic opportunity to study consciousness in humans: by injecting a short-acting anesthetic into the carotid artery of one hemisphere, clinicians can temporarily suppress that hemisphere while the other remains awake. This asymmetric manipulation offers a compelling test case for lateralized consciousness measures.
The authors analyzed EEG data from seven pre-surgical epilepsy patients undergoing Wada tests and applied a battery of consciousness measures including power spectral density, functional connectivity, and signal diversity indices. Despite clear behavioral asymmetry (patients became unresponsive on the injected side), no statistically reliable hemisphere-specific differences were found across the group in signal diversity measures.
The study introduces the concept of “cross-state unreceptiveness”—the hypothesis that contra-lateral hemisphere activity propagated via the corpus callosum may globally alter EEG dynamics, obscuring the local effects expected from a unilateral manipulation. The results highlight methodological challenges for evaluating consciousness measures using clinical populations and stimulation paradigms that may not isolate hemispheres as cleanly as assumed.
Recommended citation: Halder S, Juel BE, Sevenius Nilsen A, Raghavan LV, Storm JF. (2021). "Changes in measures of consciousness during anaesthesia of one hemisphere (Wada test)." NeuroImage. 226:117566. https://doi.org/10.1016/j.neuroimage.2020.117566
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