Graphomotor memory in Exner’s area enhances word learning in the blind

Handwriting is thought to impede vocabulary learning in sighted adults because the motor execution of writing interferes with efficient audiovisual processing during encoding. However, the motor memory of writing may facilitate adult word learning when visual sensory inputs are severely restricted. Using functional MRI, we show that late-blind participants, but not sighted participants, learned novel words by recruiting the left dorsal premotor cortex known as Exner’s writing area and its functional coupling with the left hippocampus. During later recall, the phonological and semantic contents of these words are represented in the activation patterns of the left hippocampus as well as in those of left frontotemporal language areas. These findings suggest that motor codes of handwriting help blind participants maintain word-form representations during learning and retrieval. We propose that such reliance on the motor system reflects a broad architecture of the cerebral language network which encompasses the limb motor system as a hardwired component.


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Magnetic resonance imaging
Experimental design Design type

Design specifications
Twelve late-blind participants were recruited at the Training Center for Independent Living, National Rehabilitation Center for Persons with Disabilities. A separate age-and education-matched group of 18 sighted participants were also recruited. A total of 30 participants in the present study exceed the typical sample size of fMRI research (e.g., Friston et al, Neuroimage 1999) No data were excluded from analyses.
The reproducibility of the experimental findings was verified by running data analysis multiple times; all of these attempts produced consistent results.
Random allocation of participants to experimental groups is not relevant to the present study, because our effects of interest are modeled as within-participant factors (i.e., each participant received all conditions, of which the order was counterbalanced across participants).
Blinding was not possible because both investigators and participants must understand the nature of the behavioral task used for fMRI. see above.
Twelve late-blind participants were recruited at the Training Center for Independent Living, National Rehabilitation Center for Persons with Disabilities. A separate age-and education-matched group of 18 sighted participants were also recruited.
The protocol of this study was approved by the institutional ethics committee of the National Rehabilitation Center for Persons with Disabilities.
task; event-related During the study period, participants heard each of 40 foreign-language word and their Japanese translation presented with a stimulus-onset-asynchrony of 3.5 s. On each trial, the same word pair was presented three times every 3.5 s. Trials were self-paced and separated by a brief chime sound and a silent interval of 3.5 s. During the test period  Functional and/or effective connectivity immediately after the study period, participants were presented with spoken foreign-language words and asked to translate them in Japanese.
Spoken responses during immediate recall were recorded for each condition for each participant. Participants performed the task as expected, since blind participants identified word meanings with accuracy level (SD) of 92.50 (9.65) % in the writing condition and 92.08 (10.33) % in the no-writing condition, respectively. Sighted participants performed the same task with accuracy level of 90.27 (11.04) % in the writing condition and 95.28 (6.06) % in the nowriting condition, respectively. Images from each participant were corrected for head movements, normalized to the Montreal Neurological Institute template with a 2 x 2 x2 mm3 voxel size using the linear and non-linear transformation procedure implemented in SPM12.

MNI305
Images from each participant were corrected for head movements, normalized to the Montreal Neurological Institute template with a 2 x 2 x2 mm3 voxel size and spatially smoothed with an isotropic Gaussian filter (5mm width at half maximum). These images were then high-pass filtered at 120 s and smoothed with a 4 s Gaussian kernel.
SPM12 (http://www.fil.ion.ucl.ac.uk/spm/) In the first-level univariate analysis, we computed a weighted-mean image for each condition (writing and no-writing) for each period (study and test) by fitting each voxel time-series with the known time-series of trials convolved with a canonical hemodynamic response function and its temporal derivative for each participant. In the second-level analysis, we assessed the effects of period (study vs. test), group (blind vs. sighted) and learning condition (writing vs. no-writing) using flexible factorial ANOVA implemented in SPM12, which treated these effects as fixe-effects and participants as random effects, respectively. In RSA, we constructed three theoretical representational dissimilarity matrices (motor, syllabic and semantic RDMs). For each RDM, Spearman correlation with the neural RDM for each ROI was then computed per condition per period per participant.
In both univariate analyses and RSAs, we examined neural correlates of the interaction between learning condition (writing vs. no-writing) and group (blind vs. sighted).
Unless stated otherwise, statistical significance was assessed with voxel-level p < 0.001 and cluster-level p < 0.05 corrected for multiple comparisons with family-wise error.

FWE
We performed psychophysiological interaction (PPI) analyses to assess functional connectivity with Exner's