The Neural Basis of Typewriting: A Functional MRI Study

Abstract

To investigate the neural substrate of typewriting Japanese words and to detect the difference between the neural substrate of typewriting and handwriting, we conducted a functional magnetic resonance imaging (fMRI) study in 16 healthy volunteers. All subjects were skillful touch typists and performed five tasks: a typing task, a writing task, a reading task, and two control tasks. Three brain regions were activated during both the typing and the writing tasks: the left superior parietal lobule, the left supramarginal gyrus, and the left premotor cortex close to Exner's area. Although typing and writing involved common brain regions, direct comparison between the typing and the writing task revealed greater left posteromedial intraparietal cortex activation in the typing task. In addition, activity in the left premotor cortex was more rostral in the typing task than in the writing task. These findings suggest that, although the brain circuits involved in Japanese typewriting are almost the same as those involved in handwriting, there are brain regions that are specific for typewriting.

Fig 1. A diagram of the assumptions underlying the present analysis.

(A) The cognitive model of handwriting and typing used in the present study. The labels 1, 2-W, 2-T, and 3 correspond to the labels in Fig 1B. (B) The simplified cognitive processes of typing and writing used in the present analysis. (C) The contrasts and corresponding cognitive processes. The labels 1, 2-W, 2-T, and 3 correspond to the labels in Fig 1B. Grey shading indicates conjunction contrasts.

Fig 2. Design of the typing experiment.

The typing experiment used an fMRI block design. Each session consisted of three different tasks presented pseudo-randomly in five blocks of 20-s duration. All tasks had a fixation condition. In the typing-movement task (C), subjects were instructed to type randomly with both hands when the double circle symbol was present on the monitor. fMRI: functional magnetic resonance imaging.

Fig 3. Design of the writing experiment.

The writing experiment used an fMRI block design that was almost the same as the typing experiment. Each session consisted of three different tasks presented pseudo-randomly in five blocks of 20-s duration. In the writing-movement task (C), subjects were instructed to move their right index finger randomly when the double circle symbol was present on the monitor. Subjects had practiced this task before the scan. fMRI: functional magnetic resonance imaging.

Fig 4. Positions of the keys required to type the words included in the word list.

The typing task required the subjects to type the letters corresponding to the red colored keys. The keys q, w, z, x, c, v, p, and l were excluded because there are few opportunities to press these keys for Japanese typists and these keys are located in the corners of the QWERTY keyboard.

Fig 5. Brain areas activated in the typing and writing experiments.

Each brain area was projected on a standard rendered SPM template brain. All maps were thresholded at a significance level of p < 0.05 voxel-wise corrected for multiple comparisons using family-wise error correction. (A) Typing > typing-movement contrast, (B) Typing > reading contrast, (C) Writing > writing-movement contrast, (D) Writing > reading contrast, (E) Conjunction of typing (TY) > typing movement (TM) contrast and typing (T) > reading (RE) contrast, (F) Conjunction of writing (WR) > writing movement (WM) contrast and writing (WR) > reading (RE) contrast.

Fig 6. Brain areas activated in the (TY >TM) > (WR > WM) contrast.

(A) The location of the IPS/SPL activations obtained from the (TY >TM) > (WR > WM) contrast. The map was thresholded at a significance level of p < 0.05 voxel-wise corrected for multiple comparisons using family-wise error correction. Significant activation was observed in the posterior portion of the left medial intraparietal cortex (MNI peak: -28, -60, 42; Z score = 5.32). (B) The (TY > TM) > (WR > WM) contrast activity was superimposed on a 3D rendering of a human brain. Significant activation was observed in the posterior portion of the left medial intraparietal cortex (red). CS: central sulcus, IPS: intraparietal sulcus, SF: Sylvian fissure, A: anterior, P: posterior, L: left, R: right, TY: typing, TM: typing-movement, WR: writing, WM: writing-movement.

Fig 7. Overlap of the MFG activated regions obtained from the conjunction analysis of typing and writing.

Overlap of the MFG activated regions obtained from the conjunction analysis of typing (red) and writing (blue). The green area represents the voxels that were identified in both contrasts. Overlap between two conjunctions was observed and the typing activity extended to dorsolateral and rostral region. MFG: middle frontal gyrus.