Limits...
The lesioned brain: still a small-world?

Douw L, van Dellen E, Baayen JC, Klein M, Velis DN, Alpherts WC, Heimans JJ, Reijneveld JC, Stam CJ - Front Hum Neurosci (2010)

Bottom Line: We use the IAP as a reversible model for the effect of lesions on brain network topology.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurology, VU University Medical Center Amsterdam, Netherlands.

ABSTRACT
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.

No MeSH data available.


Related in: MedlinePlus

Scatterplots of correlations between network variables and memory performance during the IAP. (A) Correlation between theta band small-worldness (S) and memory score. (B) Correlation between upper alpha band path length and memory score.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC2991225&req=5

Figure 3: Scatterplots of correlations between network variables and memory performance during the IAP. (A) Correlation between theta band small-worldness (S) and memory score. (B) Correlation between upper alpha band path length and memory score.

Mentions: Previous research has shown that network topology may be important for cognitive functioning (Micheloyannis et al., 2006a; Bosma et al., 2009; van den Heuvel et al., 2009); therefore we explored the association between network topology after injection and IAP memory score. Kendall's tau was used to correlate network features with memory score of the healthy hemisphere (i.e., after injection in the lesioned hemisphere). Results showed a significant association between better memory score and higher small-world index in the theta band after injection (Kendall's tau = 0.299, p = 0.033), and a significant correlation was present between longer upper alpha path length after injection and better memory score (Kendall's tau = 0.313, p = 0.026; see Table 3 and Figure 3). No correlations were present between memory performance and network topology before injection of amobarbital, nor were changes in topology associated with better or poorer cognitive functioning. These results indicate that more ordered networks in the theta band and longer upper alpha band path length after injection were related to better memory score.


The lesioned brain: still a small-world?

Douw L, van Dellen E, Baayen JC, Klein M, Velis DN, Alpherts WC, Heimans JJ, Reijneveld JC, Stam CJ - Front Hum Neurosci (2010)

Scatterplots of correlations between network variables and memory performance during the IAP. (A) Correlation between theta band small-worldness (S) and memory score. (B) Correlation between upper alpha band path length and memory score.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2991225&req=5

Figure 3: Scatterplots of correlations between network variables and memory performance during the IAP. (A) Correlation between theta band small-worldness (S) and memory score. (B) Correlation between upper alpha band path length and memory score.
Mentions: Previous research has shown that network topology may be important for cognitive functioning (Micheloyannis et al., 2006a; Bosma et al., 2009; van den Heuvel et al., 2009); therefore we explored the association between network topology after injection and IAP memory score. Kendall's tau was used to correlate network features with memory score of the healthy hemisphere (i.e., after injection in the lesioned hemisphere). Results showed a significant association between better memory score and higher small-world index in the theta band after injection (Kendall's tau = 0.299, p = 0.033), and a significant correlation was present between longer upper alpha path length after injection and better memory score (Kendall's tau = 0.313, p = 0.026; see Table 3 and Figure 3). No correlations were present between memory performance and network topology before injection of amobarbital, nor were changes in topology associated with better or poorer cognitive functioning. These results indicate that more ordered networks in the theta band and longer upper alpha band path length after injection were related to better memory score.

Bottom Line: We use the IAP as a reversible model for the effect of lesions on brain network topology.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurology, VU University Medical Center Amsterdam, Netherlands.

ABSTRACT
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.

No MeSH data available.


Related in: MedlinePlus