Cortical Networks for Flexible Categorisations

Lead Research Organisation: University of Glasgow
Department Name: School of Psychology

Abstract

The fundamental problem for cognitive neuroscience is to describe how perceptual and cognitive states arise from states of the brain. To understand the relationships, functional imaging techniques such as PET and fMRI can address the where question of functional anatomy: Which areas of the brain show increased activity when a particular task is being resolved and psychological functions solicited? But brain processes are not static, they are dynamic, and the questions of when and how perceptions and cognitive activities arise are as essential as where they arise. In principle, EEG and MEG provide the millisecond temporal resolution that is necessary to study the dynamics of perceptual and cognitive states. Furthermore, new developments in spatial filtering methods have recently enabled a reliable cortical localization of MEG signals, which are less distorted by the intervening tissue than EEG signals. Lastly, and central to this research proposal, high temporal resolution allows for an optimal decomposition of the measured MEG signals into frequency components, in order to analyse oscillatory activity and coupling in relation to cognitive tasks. Here, we will render the a flow-chart of information processing in the brain for the main nodes of the cortical processing networks associated with biologically important face categorisation tasks (i.e. gender and expression).

Technical Summary

A proposal with a long history suggests that the dynamics of psychological states is related to the oscillatory activity of the neural substrate (see VanRullen & Koch, 2003; Ward, 2003, for recent reviews). Simply stated, synchronized discharges of cortical cell assemblies with a prominent rhythmicity would be the neural correlates supporting discrete cognitive and perceptual states. This is based on evidence of a consistent relationship between behavioural variables and the frequency of both the theta (4-8 Hz) and alpha rhythms (8-12 Hz) in memory and perceptual tasks. An important task, then, it is ascribe information content to the measurable parameters of oscillatory brain activity. Here, we will for the first time merge methods to identify the form of cognitive states and ascribe them information content. To isolate form, we will use the proven MEG DICS methods for localising oscillatory cortical networks (e.g. Gross et al., 2001; Gross et al., 2004). For ascribing content, we will use Bubbles (Schyns et al., 2003; Smith et al., 2004; Smith et al., 2005). To tap into biologically important cortical information processing networks we will use biologically-relevant face categorization tasks (e.g. gender and categorization of expressions). Our goal is to provide a flow-chart of information processing in the brain for the main nodes of the cortical processing networks associated with each one of the face categorization tasks tested.

Publications


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Description Cognitive neuroscience assumes a correspondence between specific spatio-temporal patterns of neural activity and the states of a
mechanism that processes cognitive information. Mechanistic explanations of cognition should therefore translate patterns of neural activity into the components of a formal mechanism: a set of information processing states and their transitions. For the first time, we carried out this research programme with four naive observers instructed to categorise randomly presented face information. With classification image techniques, we revealed the diagnostic features that the brain requires to produce correct behaviour (i.e., two eyes for gender categorisation in one session; the mouth for expression in the other session). With the same techniques applied to brain signals, we revealed the features processing states associated with modulations of oscillatory
EEG energy (measured on occipito-temporal face-sensitive electrodes). We showed how transitions between distinct feature processing statesin the theta/alpha [4-12 Hz] oscillatory bands implement two face categorisations. On the left and right occipito-temporal electrodes of each observer, processing of the contra-lateral eye precedes bilateral integration of the features required for behaviour. For the first time, we related stimulus information to behaviour via sequences of categorisation-specific feature processing states in the brain.
Exploitation Route Analyses of cognitive tasks will ultimately require a set of causal-functional states that relation stimulus to behavior. We provided a methodology to understand what these states are and how they transform.
Sectors Healthcare