Mapping The Functional Anatomy of Reading

Manzar Ashtari PhD, Kenneth R. Perrine PhD, Rania Elbaz BA, Uzma Syed BS, Allan B. Ettinger MD, Alexandra E. McBride MD and Alan Diamond MD

fMRl was performed in fourteen right handed subjects to locate the lexical reading centers. Visual stimuli were presented using MR compatible video goggles. fMR images were acquired on I.5 Tesla system using the bold technique. Group and individual analysis were carry out using SPM96. Each individual subject showed strong left lateralized activations in several areas relating to language generation and comprehension. Group analysis revealed areas of activation primarily located in the similar areas. The most striking finding was the activation of the tempro-parietal region. This task offers tremendous potential for pre-surgical evaluation of neurosurgical patients with lesions located in essential cortical regions of reading.

Purpose: To identify brain regions involved in the functional anatomy of reading in normal controls and apply the results to pre-surgical planning of patients with epilepsy or temporal lobe tumor. Methods and Materials: We studied fourteen right handed (as assessed by the Edinburgh Handedness Inventory) healthy volunteers (6 M/8 F, mean age q 31.6 , rang q 23 - 49 ). Stimuli were programmed in E-Prime (Psychology Tools, Pittsburgh) and presented to the subjects using MR compatible Vision-2000 (Resonance Technology Northridge, CA) video goggles. In the reading condition, simple unfinished sentences (all upper case) were presented to the subjects with a blank space at the end. Subjects were asked to complete the sentences by filing the blank with an appropriate word. In an attempt to subtract the non-reading components of the task, active blocks were alternated with control blocks of letter strings. Similar to active blocks, subjects were presented with a string of letters (all upper case) where a letter was missing. Subjects were asked to find the sequence of the letters and fill in the missing one. In addition to the letter condition, resting control blocks were used to contrast with active reading comprehension epochs. During rest blocks no other stimuli were presented other than the background scanner noise and subjects were not required to make any response. Sentences and letters were presented at a rate of one every 3 second with one second between them, for a total of 10 sentences or 10 letter strings. The rest blocks were 20 seconds in length. A total of four active, four control, and eight rest blocks constituted a run, for a total task duration of eight minutes and sixty seconds. Additionally, a sixteen second rest block preceded all other blocks to allow for spin equilibrium. MR Acquisition: All MR images were obtained on a GE Horizon EchoSpeed with the slew rate of 120Tlmlsec operating at 1.5 Tesla. Functional MR images were acquired using the bold technique and a single shot EPI gradient echo sequence (TR q 4000 msec, TE = 50 msec, 64x 64 matrix, 22 cm FOV, and BW 64) to obtain 23 contiguous 5mm slices covering the whole brain. To superimpose the activation on high resolution MR images, a T2 weighted fast spin echo sequence was acquired in the same imaging session to cover the exact same slice locations of the fMRl time series. Data Analysis: Group and individual analysis was perfoned using SPM96 software (Welcome Department of Cognitive Neurology, London. UK) using the general linear model. Images were realigned, normalized to a T2 weighted template created by the Montreal Neurologic Institute (MNI) and smoothed with a gusian filter of 7mm in all directions. The statistical analysis was based on two temporal basis functions and activation maps were set at a high threshold of p= 0.001 and corrected p value of 0.05. Results are presented as z-maps on the SPM 96 canonical SPGR brain images. We assessed four different contrasts of Reading - Rest (RE-R), Reading - Letter (RE-L), Letter - Rest (L-R), and Letter - Reading (L-RE).

Results: Statistical analysis was carried out for individual subjects as wel as averaged group analysis. Each individual subject had strong left lateralized activations in the inferior frontal gyrus (Broca’s region (BA #44) triangular area (BA #45) that is closely related to opercular and Brcca’s area and visual cortex (BA # 17, 18)) the posterior temporal (BA #22) and angular gyrus (BA #39) regions, and an overlapping area including Supplementary Motor Area, or SMA, (mesial aspect BA #6) and the ventral cigulate gyrus (BA #24). Group analysis for RE - R contrast revealed areas of activation primarily located in the similar areas. Contrast RE - L, however, demonstrates the primary areas involving the lexical aspect of reading such as posterior temporal, angular and supra- marginal gyri (Fig.1). As is depicted in Fig.1, there are no activations involving the bilateral Broca’s area, bilateral frontal eye fields and parietal occipital areas responsible for eye motions and scanning a line of text. These areas are clearly presented in contrast L - R as shown in Fig.2. The most striking finding of this study was the strong activation of the posterior tempro-parietal region shown in Fig.1. Conclusion: fMRl demonstrates a let? lateralized neuronal network for reading processes involving the angular gyrus, posterior superior tempora gyrus, and inferior frontal gyrus The posterior tempro-parietal activation corresponds to areas known from prior lexical studies and cortical mapping to mediate lexical aspects of reading. Reading involving true lexical processing contrasted with letter string as control blocks that stimulate similar areas but not involving the primary reading areas may bf useful to reveal the pure reading components of the task. This task offers tremendous potential for presurgical evaluation of neurosurgical patients with lesions located in essential cortical regions of reading. This is especially important in cases where circumstances may prevent intraoperative cortical mapping. The information gained from fMRl enable! the surgeon to remove lesions and avoid areas with significant language activations. We have implemented this procedure successfully on severa neurosurgical candidates in our institution.

FIG 1: READING - LETTER

FIG 2: LETTER - REST