Interhemispheric differences of spectral power in expressive language: A MEG study with clinical applications

Abstract

In the last decade we have seen an exponential growth of functional imaging studies investigating multiple aspects of language processing. These studies have sparked an interest in applying some of the paradigms to various clinically relevant questions, such as the identification of the cortical regions mediating language function in surgical candidates for refractory epilepsy. Here we present data from a group of adult control participants in order to investigate the potential of using frequency specific spectral power changes in MEG activation patterns to establish lateralisation of language function using expressive language tasks. In addition, we report on a paediatric patient whose language function was assessed before and after a left hemisphere amygdalo-hippocampectomy. Our verb generation task produced left hemisphere decreases in beta-band power accompanied by right hemisphere increases in low beta-band power in the majority of the control group, a previously unreported phenomenon. This pattern of spectral power was also found in the patient's post-surgery data, though not her pre-surgery data. Comparison of pre and post-operative results also provided some evidence of reorganisation in language related cortex both inter- and intra-hemispherically following surgery. The differences were not limited to changes in localisation of language specific cortex but also changes in the spectral and temporal profile of frontal brain regions during verb generation. While further investigation is required to establish concordance with invasive measures, our data suggest that the methods described may serve as a reliable lateralisation marker for clinical assessment. Furthermore, our findings highlight the potential utility of MEG for the investigation of cortical language functioning in both healthy development and pathology.

Changes in Theta and Beta Oscillations as Signatures of Novel Word Consolidation

“…The late time window, extending past the end of the analyzed epoch, and the central distribution of this effect point to a response-related explanation. Beta desynchronization over central channels has often been linked to motor preparation and imagery, both of limbs (De Lange, Jensen, Bauer, & Toni, 2008) and of speech (Piai, Roelofs, & Maris, 2014;Fisher et al, 2008), and has been shown to increase with response certainty (Alegre et al, 2004). Given that untrained novel words did not activate a representation based on which a response could be prepared, but existing words did, the larger desynchronization response to untrained existing versus novel words may reflect selective motor preparation for the existing words.…”

Is there a common oscillatory brain mechanism for producing and predicting language?

“…In the present paper, we focus on the parallel between production and prediction in language, based on the dynamic principles of forward modeling a motor command. Given the relevance of beta band activity in the motor domain and the importance of motor planning for articulation, it is not surprising to observe that a number of studies have reported beta band effects related to speech production (Fisher et al, 2008;Singh, Barnes, Hillebrand, Forde & Williams, 2002). Recently, Findlay et al (2012) employed a verb generation task in which participants were presented with a noun and had to produce a related verb.…”

Language mapping in children using resting-state functional connectivity: comparison with a task-based approach

“…1,5 Consequently, inconclusive results are reported in most patients younger than age 10 for ESM (up to 81%) and for IAT (50%). 5,6 In the past decade, noninvasive neuroimaging techniques, including functional magnetic resonance imaging (fMRI) [7][8][9][10][11] and magnetoencephalography (MEG), [12][13][14][15][16][17][18] have been widely used for language cerebral lateralization and mapping in adults and children. These techniques show very good concordance with invasive procedures (IAT and ESM) for language dominance and localization.…”