Year: 2005
Type: dissertation
Abstract: At the neuronal population level, temporally correlated activities can be observed as network oscillations and synchrony.In the mammalian brain, oscillations in specific frequency bands are thought to have distinct functional roles, although the precise identities of these functions have largely remained under debate.In the adult brain, fast network oscillations in beta-(14-30 Hz) and gamma-(30-80 Hz) frequency bands appear to provide a means for integrating anatomically distributed processing and have hence been associated with psychological-level phenomena such as feature binding and object representation, as well as with perception, attention and short-term memory.The physiological basis of this notion rests on the fact that the synchronized firing of action potentials involved in such fast oscillations is very powerful both in entraining neuronal target populations as well as in inducing synaptic plasticity.Cognition and brain function in general, however, also involve greater time scales, from "cognitive quanta" of ~100-150 ms to > 10 s fluctuations in psychophysical task performance.Interestingly, the cognitive quanta may be linked to neuronal oscillations in the theta-(4-8 Hz) / alpha-(8-14 Hz) frequency bands and the very slow fluctuations, respectively, to ~0.1 Hz oscillations presented in this Thesis.How do the neuronal phenomena with these widely separated time scales interact?The studies in this Thesis show that cross-frequency phase and amplitude interactions are abundant in both the developing and adult brain.Neuromagnetic recordings from the adult human subjects revealed that throughout the range from 3 to 80 Hz, oscillations with frequency ratios of 1:2-1:4 were partially 1:n phase synchronized.In these subjects, mental arithmetic tasks enhanced specifically the 1:2-1:4 phase synchronies among oscillations in gamma-, beta-, and alpha-frequency bands.The amplitudes of all observed oscillations were also weakly coupled, but the cognitive tasks suppressed these correlations.In direct-current coupled electroencephalogram (DC-EEG) of sleeping adults, another form of cross-frequency phase interaction was observed.The amplitude envelope of oscillations from 1 to 30 Hz was strongly modulated by the phase of a novel infraslow oscillation with a frequency ranging from 0.02 to 0.2 Hz.Such nestedness is classically known to take place between rat hippocampal gamma (20-100 Hz) and theta (4-12 Hz) oscillations.In in vitro recordings from newborn rat hippocampus, pyramidal cell spiking reached population rates of > 100 spikes/s.This population activity was observed in bursts recurring at 20-80 Hz during the endogenous activity transients that dominate the activity of developing cortical structures.Finally, in DC-EEG of preterm human babies, large-amplitude oscillations in several distinct frequency bands from 0.1 to 30 Hz were concentrated into massive activity transients that in many aspects were similar to those observed in newborn rat cortex.In the light of these data, the cross-frequency phase interactions in the adult brain appear to have a fundamental role in cross-hierarchical and -functional integration and modulation.In the developing cortex, the precise temporal patterning and nested oscillations within the population bursts could underlie spike-timing dependent shaping of network connectivity with the same coding strategies that later in life are utilized in feature integration and higher cognitive operations.
Source: Työväentutkimus Vuosikirja
Author: J. Matias Palva
Language: English
Subfield: Cognitive Neuroscience
Field: Neuroscience
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W2141279099