Introduction

A large part of our current knowledge about cognitive brain functions results from studies of the modular approach which classifies brain areas as independent units responsible for complex cognitive functions. However, brain imaging studies of the last decade have shed light on the limitations of this approach and especially on the general conclusions based on modular explanations, showing that a re-evaluation of the role and function of brain areas including those seen as pinnacles of modularity (e.g. primary sensory areas) is needed. Therefore, the era of simplistic views about mapping cognitive constructs onto individual brain areas is over. New insights into cognitive functions including language are provided by studying the conjoint functions of brain areas working within the concerted action of large-scale networks. A great step towards a high-complexity approach results from recent investigations into sophisticated methods.

The concept of brain networks that has been rediscovered by recent neuroscience has emerged from research data on the structural connectivity and functional interdependence of specialized networks formed by the anatomical linkage of the corresponding neurons. There are various neuronal populations with internal circuitry configurations throughout the brain, and some of these act as network nodes. Network nodes are defined as neuronal assemblies of local structural organization with large-scale structural connectivity and local functional activity different from those of their neighbours. The functional interdependence of brain network nodes refers to joint activity in different brain structures that are co-dependent according to their functional and/or behavioural parameters. Nodes of large-scale functional networks are described by functional neuroimaging studies using the functional magnetic resonance imaging (fMRI) blood oxygen level dependent (BOLD) signal, by relating the joint activation of brain areas to different cognitive functions. More than two decades ago, Mesulam (1990) described the brain network concept, as well as providing a thorough analysis of anatomically distinct large-scale brain networks responsible for different cognitive functions. However, it is still an open question as to how cognitive functions and especially languages are served by large-scale brain networks.