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Original Research ARTICLE

Front. Hum. Neurosci., 11 November 2010 | http://dx.doi.org/10.3389/fnhum.2010.00174

The lesioned brain: still a small-world?

  • 1 Department of Neurology, VU University Medical Center, Amsterdam, Netherlands
  • 2 Department of Neurosurgery, VU University Medical Center, Amsterdam, Netherlands
  • 3 Department of Medical Psychology, VU University Medical Center, Amsterdam, Netherlands
  • 4 Department of Clinical Neurophysiology and The Epilepsy Monitoring Unit, Dutch Epilepsy Clinics Foundation, Heemstede, Netherlands
  • 5 Department of Psychology, Dutch Epilepsy Clinics Foundation, Heemstede, Netherlands
  • 6 Department of Neurology, Academic Medical Center, Amsterdam, Netherlands
  • 7 Department of Clinical Neurophysiology, VU University Medical Center, Amsterdam, Netherlands

The intra-arterial amobarbital procedure (IAP or Wada test) is used to determine language lateralization and contralateral memory functioning in patients eligible for neurosurgery because of pharmaco-resistant epilepsy. During unilateral sedation, functioning of the contralateral hemisphere is assessed by means of neuropsychological tests. We use the IAP as a reversible model for the effect of lesions on brain network topology. Three artifact-free epochs (4096 samples) were selected from each electroencephalogram record before and after amobarbital injection. Functional connectivity was assessed by means of the synchronization likelihood. The resulting functional connectivity matrices were constructed for all six epochs per patient in four frequency bands, and weighted network analysis was performed. The clustering coefficient, average path length, small-world index, and edge weight correlation were calculated. Recordings of 33 patients were available. Network topology changed significantly after amobarbital injection: clustering decreased in all frequency bands, while path length decreased in the theta and lower alpha band, indicating a shift toward a more random network topology. Likewise, the edge weight correlation decreased after injection of amobarbital in the theta and beta bands. Network characteristics after injection of amobarbital were correlated with memory score: higher theta band small-world index and increased upper alpha path length were related to better memory score. The whole-brain network topology in patients eligible for epilepsy surgery becomes more random and less optimally organized after selective sedation of one hemisphere, as has been reported in studies with brain tumor patients. Furthermore, memory functioning after injection seems related to network topology, indicating that functional performance is related to topological network properties of the brain.

Keywords: small-world networks, Wada test, functional connectivity, brain network, graph theory

Citation: Douw L, van Dellen E, Baayen JC, Klein M, Velis DN, Alpherts WCJ, Heimans JJ, Reijneveld JC and Stam CJ (2010) The lesioned brain: still a small-world? Front. Hum. Neurosci. 4:174. doi: 10.3389/fnhum.2010.00174

Received: 16 June 2010; Paper pending published: 09 July 2010;
Accepted: 19 August 2010; Published online: 11 November 2010.

Edited by:

Francisco Barcelo, University of Illes Balears, Spain

Reviewed by:

Danielle S. Bassett, University of California at Santa Barbara, USA
Nazareth Castellanos, Universidad Politécnica de Madrid, Spain

Copyright: © 2010 Douw, van Dellen, Baayen, Klein, Velis, Alpherts, Heimans, Reijneveld and Stam. This is an open-access article subject to an exclusive license agreement between the authors and the Frontiers Research Foundation, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are credited.

*Correspondence: Linda Douw, Department of Neurology (2F-019), VU University Medical Center, PO Box 7057, 1007 MB Amsterdam, Netherlands. e-mail: l.douw@vumc.nl