Dynamic network structure of interhemispheric coordination

Abstract

Fifty years ago Gazzaniga and coworkers published a seminal article that discussed the separate roles of the cerebral hemispheres in humans. Today, the study of interhemispheric communication is facilitated by a battery of novel data analysis techniques drawn from across disciplinary boundaries, including dynamic systems theory and network theory. These techniques enable the characterization of dynamic changes in the brain's functional connectivity, thereby providing an unprecedented means of decoding interhemispheric communication. Here, we illustrate the use of these techniques to examine interhemispheric coordination in healthy human participants performing a split visual field experiment in which they process lexical stimuli. We find that interhemispheric coordination is greater when lexical information is introduced to the right hemisphere and must subsequently be transferred to the left hemisphere for language processing than when it is directly introduced to the language-dominant (left) hemisphere. Further, we find that putative functional modules defined by coherent interhemispheric coordination come online in a transient manner, highlighting the underlying dynamic nature of brain communication. Our work illustrates that recently developed dynamic, network-based analysis techniques can provide novel and previously unapproachable insights into the role of interhemispheric coordination in cognition.T he field of split-brain research began several decades ago with the use of a drastic surgical solution for intractable epilepsy (1-3): the severing of the corpus callosum. This procedure significantly decreased the connectivity between the hemispheres, thereby irrevocably altering interhemispheric communication. Although a few interhemispheric pathways remained through subcortical structures and the anterior commissure, examination of callosal function using split visual field experiments clearly demonstrated its role in interhemispheric communication (2). The callosal projection plays a particularly crucial role in a variety of sensory-motor integrative functions of the two hemispheres (4), shows changes with age, and demonstrates the potential for dynamic changes with training (5). In fact, experiments in patients with severance of the callosum revealed that it subserves a large range of behaviors and cognitive functions that underlie the varied workings of the mind.Interhemispheric communication has been studied using two basic approaches. The first uses behavioral experiments to examine cognitive phenotypes, and the second uses neuroscientific experiments to examine brain phenotypes. Split-brain research initially focused on the former: Patients demonstrated striking behavioral phenotypes that provided clues regarding the underlying mechanics of brain communication. For example, although most perceptual processing appears to be isolated in each hemisphere following surgery, some attentional and emotional mechanisms initiated in one hemisphere can still be communicated to the other, cortically disconnected,...

Robust detection of dynamic community structure in networks

“…that can vary in time. 12,56 E. Data set 2: Behavioral networks Our second data set contains ordered nodes that remain unchanged in time. The network topology in this case is highly constrained, as edges are only present between consecutive nodes.…”

“…2 The formalism of temporal networks is convenient for studying data drawn from areas such as person-to-person communication (e.g., via mobile phones 5,6 ), one-to-many information dissemination (such as Twitter networks 7 ), cell biology, distributed computing, infrastructure networks, neural and brain networks, and ecological networks. 2 Important phenomena that can be studied in this framework include network constraints on gang and criminal activity, 8,9 political processes, 10,11 human brain function, 4,12 human behavior, 13 and financial structures. 14,15 Time-dependent complex systems can have densely connected components in the form of cohesive groups of nodes known as "communities" (see Fig.…”

Spectral properties of the temporal evolution of brain network structure

“…It has been proposed that characterizing the temporalevolution properties of the brain network during different cognitive states is crucial to understanding a large variety of complex processes, from cognitive process dynamics to brain disease. 1,13,14 Despite growing interest in these dynamic networks as a new modality for understanding information processing, development, and disease, their temporal characteristics have not been well characterized. The characterization of dynamic brain network properties has received great interest for the study of brain neural mechanisms.…”

Multiscale topological properties of functional brain networks during motor imagery after stroke

“…Specifically, based on the peculiarity of functional brain networks that are to be embedded in a physical space that is coincident with the anatomic substrate (Honey et al, 2007;Doron et al, 2012), we aimed to characterize the FC patterns on several scales: i) the entire brain (large scale), ii) the 2 hemispheres (intermediate scale), and iii) each node in the 2 hemispheres (small scale). This framework was adopted to describe the possible brain connectivity disturbances in stroke.…”