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The left frontal aslant tract is important for written communication irrespective of handedness

Henrietta Howells1*, Stephanie Forkel1, Flavio Dell'Acqua1, Anoushka Leslie1, Andy Simmons2, Declan Murphy3 and Marco Catani1
  • 1 King's College London, Institute of Psychiatry, Psychology and Neuroscience, United Kingdom
  • 2 King's College London, Centre for Neuroimaging Sciences, United Kingdom
  • 3 King's College London, Institute of Psychiatry, Psychology and Neuroscience, United Kingdom

Written communication has facilitated the sharing of information within and across generations. Dyspraxia and writing difficulties are common in children and can severely impede academic progression. Hence understanding the neural basis of written communication is essential to characterise neurodevelopmental disorder and develop treatment. Recent meta-analyses have synthesised decades of neuropsychological, lesion and functional imaging studies to show a ventral 'central' system for processing phonological and orthographic content overlaps with the left perisylvian language network, and is anatomically segregated from a 'peripheral' system for planning and execution that recruits widespread left superior parieto-frontal regions (Rapp, 2015; Purcell, 2011; Planton, 2013). The frontal aslant tract connects inferior frontal regions with superior frontal regions, the supplementary motor area (SMA) and pre-SMA, and U-tracts connect this with Exner's area (Catani, 2012). Research suggests this tract is important for verbal fluency in right handers, and is impaired in those who stutter (Catani, 2013; Kemerdere, 2016), but it is unknown whether this tract may also be important for orthographic fluency. We set out first to evaluate whether there are associations between this tract and performance in writing tasks in right handers. We also compared whether there is a similar hemispheric organisation in left handers. Thirty healthy subjects were scanned (16 female, mean age 27.6±4 years) on a 3T GE MRI scanner (voxel size 2.4x2.4x2.4mm, 128x128 matrix, field of view 307x307mm, 60 slices, b-value 3000 s/mm2, 60 diffusion-weighted directions and 7 non diffusion-weighted volumes). We corrected for motion and eddy current distortions using FSL (Smith, 2004) and processed the data for whole brain spherical deconvolution tractography using StarTrack (www.natbrainlab.com). 12 subjects were classified as left-handed (18 subjects right-handed) based on their preference for unimanual activities, which corresponded with their writing hand. Virtual in-vivo dissections were performed of the frontal aslant tract (FAT) in each hemisphere. Tract specific measurements were extracted. Subjects performed a handwriting assessment adapted from the Detailed Assessment of Speed of Handwriting (DASH) to identify inter-individual differences in handwriting speed (letters per second) and graphomotor co-ordination (GMC; Barnett, 2007). There was no significant difference between right and left-handers in dominant hand performance, whether speed (F(7,18)=1.9, p=0.5) or GMC (F(7,18)=0.2, p=0.6). No hemispherexhandedness interaction was evident for FAT diffusion measurements. Left FAT volume was significantly positively correlated with writing speed in right-handers (r=0.6, p=0.009) and in left-handers (r=0.6, p<0.05). There was no correlation between the right FAT and writing speed in right- or left-handers. Grouping right- and left-handers, a highly significant correlation existed between GMC and left FAT volume (r=0.6, p<0.001). There was a highly significant correlation between writing speed and left FAT HMOA (positive: r=0.5, p<0.005) and mean diffusivity (negative: r=-0.4, p<0.03). There were no significant associations between writing performance and the FAT in the right hemisphere. Our results show that inter-individual differences in writing fluency are associated with structural differences in the left frontal aslant tract. This tract may indeed be important for written as well as verbal fluency. We suggest this tract mediates communication between the central and peripheral handwriting networks in the left hemisphere irrespective of handedness.

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References


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Keywords: handwriting, handedness, tractography, verbal fluency, diffusion imaging, frontal lobe connectivity

Conference: 54th Annual Academy of Aphasia Meeting, Llandudno, United Kingdom, 16 Oct - 18 Oct, 2016.

Presentation Type: Poster Sessions

Topic: Student Submissions

Citation: Howells H, Forkel S, Dell'Acqua F, Leslie A, Simmons A, Murphy D and Catani M (2016). The left frontal aslant tract is important for written communication irrespective of handedness. Front. Psychol. Conference Abstract: 54th Annual Academy of Aphasia Meeting. doi: 10.3389/conf.fpsyg.2016.68.00033

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Received: 26 Apr 2016; Published Online: 15 Aug 2016.

* Correspondence: PhD. Henrietta Howells, King's College London, Institute of Psychiatry, Psychology and Neuroscience, London, London, SE5 8AF, United Kingdom, etta.howells@gmail.com