On the Physiological Modulation and Potential Mechanisms Underlying Parieto-Occipital Alpha Oscillations

Abstract

The parieto-occipital alpha (8–13 Hz) rhythm is by far the strongest spectral fingerprint in the human brain. Almost 90 years later, its physiological origin is still far from clear. In this Research Topic I review human pharmacological studies using electroencephalography (EEG) and magnetoencephalography (MEG) that investigated the physiological mechanisms behind posterior alpha. Based on results from classical and recent experimental studies, I find a wide spectrum of drugs that modulate parieto-occipital alpha power. Alpha frequency is rarely affected, but this might be due to the range of drug dosages employed. Animal and human pharmacological findings suggest that both GABA enhancers and NMDA blockers systematically decrease posterior alpha power. Surprisingly, most of the theoretical frameworks do not seem to embrace these empirical findings and the debate on the functional role of alpha oscillations has been polarized between the inhibition vs. active poles hypotheses. Here, I speculate that the functional role of alpha might depend on physiological excitation as much as on physiological inhibition. This is supported by animal and human pharmacological work showing that GABAergic, glutamatergic, cholinergic, and serotonergic receptors in the thalamus and the cortex play a key role in the regulation of alpha power and frequency. This myriad of physiological modulations fit with the view that the alpha rhythm is a complex rhythm with multiple sources supported by both thalamo-cortical and cortico-cortical loops. Finally, I briefly discuss how future research combining experimental measurements derived from theoretical predictions based of biophysically realistic computational models will be crucial to the reconciliation of these disparate findings.

Connecting occipital alpha band peak frequency, visual temporal resolution, and occipital GABA levels in healthy participants and hepatic encephalopathy patients

“…In humans, a reasonable number of studies show effects of pharmacological GABAergic modulation on occipital oscillatory alpha band activity (e.g., Schreckenberger et al, 2004 ; Ahveninen et al, 2007 ). However, these studies almost exclusively focus on oscillatory power (reviewed by Lozano-Soldevilla, 2018 ), whereas modulations of peak frequency are rarely reported (but see Liley et al, 2003 ). Mechanistic models of thalamic generators driving the frequency of cortical alpha band activity by means of GABA-mediated conductance changes at 10 Hz have been recently put forward and related to visual stimulus processing ( Gips et al, 2016 ).…”

Inferring a simple mechanism for alpha-blocking by fitting a neural population model to EEG spectra

“…Despite the importance of alpha blocking in studies of cognition, it still lacks a 9 generally-accepted, mechanistic understanding [8]. Importantly, the mechanism 10 associated with alpha blocking is usually considered separately from the mechanism 11 associated with alpha wave generation.…”

“…More generally, changes in alpha-band power can be 6 effected by a range of visual, tactile and auditory stimuli and altered states of arousal 7 and is widely used as a diagnostic of cognitive activity [4-7]. 8Despite the importance of alpha blocking in studies of cognition, it still lacks a 9 generally-accepted, mechanistic understanding [8]. Importantly, the mechanism 10 associated with alpha blocking is usually considered separately from the mechanism 11 associated with alpha wave generation.…”

Evidence that alpha blocking is due to increases in system-level oscillatory damping not neuronal population desynchronisation

“…Classically clear alpha-band oscillations can be seen in occipital cortex (the classical alpha rhythm), central Rolandic areas (the so called mu rhythm) and mid-temporal regions (the so called 'third rhythm') (Chang et al, 2010). However, despite many decades of investigation involving the alpha rhythm and its physiological basis and cognitive correlates, little certainty has been achieved regarding its generative mechanisms and functional roles (Lozano-Soldevilla, 2018).…”