Alterations of language related oscillatory activity and spontaneous neural dynamics after stroke Kielar, A., Deschamps, Chu, R., Jokel, R., and Meltzer, J. A. Rotman Research Institute, Baycrest Centre University of Toronto
Introduction
BA 6/9
MEG Mapping of Semantic and Syntactic Processing
•Damage to the LH perisylvian regions is associated with impaired ability to produce or comprehend language, referred to as aphasia
Semantic violation-control Left Right
•Considerable changes in the cortical representation of language can occur following stroke, and recovery is assumed to occur as a result of cortical reorganization in structurally intact brain tissue (Saur et al., 2006; Thompson et al., 2008)
•This increase in spontaneous slow-wave activity is thought to originate from the “perilesional” tissue that is functionally compromised, but contains living neurons
Right
0
Young Controls (YC)
6
3
9
Voxel-Lesion Symptom Mapping (VLSM)
A.
Semantic Anomalies
Syntactic Anomalies
p =.001
p = .01
8-30Hz ERS
Older Controls (OC) B. p = .01
Power (AU)
•Quantification of this dysfunctional electrical activity has the potential to serve as a biomarker of neuronal (dys)function after stroke. •Resting state analysis can be used to identify preserved networks and brain areas with potential for re-recruitment in the course of the recovery/treatment
Left
Stroke Lesion extent
BA 45/46
•It is not clear whether the recovery of different linguistic components of language, such as semantics and syntax, engages distinct or overlapping processes and brain networks. •Stroke is associated with electrophysiological abnormalities in perilesional tissue: • Spectral slowing (Butz et al., 2004; Meinzer et al., 2004) • Reduction in entropy of the neural signal (Chu et al., 2015, Tecchio et al., 2005)
Syntactic violation-control
p =.001
Stroke (STP)
Present study:
8-30Hz ERD
•Applied MEG to characterize perilesional and contralesional activity in processing of semantic and syntactic information in patients with aphasia.
p = .01
p = .01
p = .01
LMTG
80
Lesion percentage
• Both left and right hemispheres are thought to support language recovery. However, the relative contributions of each hemisphere and the neural mechanisms mediating successful recovery are not well understood (Brieier et al. 2009; Crinion et al., 2007).
Behavioral Performance
Results
LMTG
80
rho(16) = -.529, p < .05
rho(16) = -.538, p < .05
60
60
40
40
20
20
0 0.00
1.00
2.00
3.00
-20
4.00
0 -1.00 -20
d’ score semantic
0.00
1.00
2.00
3.00
4.00
d’ score syntactic
•Mapped stroke-related functional changes
A. VLSM analyses evaluate relationship between lesion location and language impairment on the MEG task. For semantic anomalies, reduced accuracy was associated with lesions in the LMTG and LSTG, extending into the LAG. For syntactic anomalies, the analysis identified a smaller cluster in the LSTG.
•Assessed the possibility of compensatory reorganization of language to contralesional hemisphere regions
B. Relationship between MEG task accuracy and lesion extent in cortical ROIs. Lesion extent in the LMTG correlated with comprehension performance across participants.
Group Comparison Maps (8-30Hz ERD differences)
STP vs. AM
•Investigated the relation between MEG activation pattern and sentence comprehension performance •Mapped distribution of spontaneous slow-wave activity and resting neural dynamics
Correlation between MEG activity and Sentence Comprehension Performance Stroke vs. Controls (8-30Hz Power) Stoke Participants (n =Semantic 11) 8-30Hz ERD vs. Accuracy on semantic anomalies Syntactic 8-30Hz ERD vs. Accuracy on syntactic anomalies Stroke vs. Controls Perfusion Data (Cerebral Blood Flow (mL blood/100g tissue/minute measured with ASL)
Method n = 17 stroke survivors with aphasia (Age: M = 65, 46-84y, Ed: 16.58) n = 17 age-matched adults (Age: M = 65, 45-80y, Ed: 17 ) n = 21 young adults (Age: M = 25, SD = 3: Ed: 16)
p = .01
p = .01
1
Task: Acceptability Judgment Task
0 Spearman’s Rho
•Patients recruited RH anterior frontal and dorso-lateral frontal cortex that was not activated in controls
-1
Resting State MEG Effect of Stroke
500 ms
Stroke vs. YC
Effect of Aging Stroke vs. AM
400 ms
AM vs. YC
350 ms
MSE scales 1-5
•Activity in the posterior superior temporal cortex correlated with higher accuracy on semantic and syntactic tasks, suggesting a supportive role of this region in recovery of these linguistic functions
Language Stimuli (based on Block and Baldwin, 2010)
Syntactic Anomaly: She will going to the bakery for a loaf of bread. Control: She will go to the bakery for a loaf of bread.
151axial gradiometers,
Alpha (8-12Hz)
• Resting data: We found that the perilesional neural tissue produced abnormal slow-wave activity and reduced entropy indicating the extent of ”functional lesions”
whole-head coverage Sampling rate: 625 Hz MEG data was coregistered with T1-weighted MRI using markers on fiducial points. Data was analyzed with Synthetic Aperture Magnetometry (SAM, Vrba and Robinson, 2001). Resting Scan: 5 minute spontaneous measurement in MEG Measured: Relative power from power spectra in delta (1-4Hz), theta (5-7Hz), alpha (8-12Hz), and beta (1530Hz) frequency bands (Poza et al., 2007) Multiscale Entropy (MSE): Reflects complexity of neural signal. Decreased MSE values indicate neuronal dysfunction (Costa et al., 2005, Park et al., 2007)
•Better recovery of semantic processing is associated with recruitment of the RH components of the ventral network
•Some of the activated regions may reflect upregulation of non-linguistic domain-general processes (Brownsett et al., 2014; Meltzer et al., 2013)
Delta (1-3Hz)
CTF Omega MEG system
•Correlation analyses indicated that recruitment of posterior RH areas is associated with better semantic performance, whereas higher accuracy on syntactic task was related to bilateral superior temporo-parietal and right frontal activity.
•Recovery of syntax is mediated by components of the dorsal network, bilaterally
350 ms
Semantic Anomaly: She will go to the bakery for a loaf of books.
•Language data: In the presence of a lesion, language networks recruit available brain regions in both hemispheres, and the specific pattern of activation depends on the type of linguistic information being processed •For semantic anomalies, patients activated LH regions adjacent to the lesion, as well as RH areas homologous to the parietal and temporal areas that were activated in controls
Participants:
400 ms
Discussion
Beta (15-30Hz) p = 0.01
p = 0.01
Funded By
• VLSM analysis: Damage to the LpSTG/MTG and AG was associated with sentence comprehension impairment, suggesting an important role for this region in language comprehension
p = 0.01
Contact
[email protected]
References Available from authors under separate cover
