The feasibility of 2-back task with alphabets and functional transcranial Doppler sonography in assessing hemispheric lateralization of working memory in Chinese

Background: Hemispheric asymmetry studies of working memory are mainly carried out in western countries. Data on Chinese is limited in this area of research. On the other hand, working memory assessment can be limited by the temporal resolution of the imaging modality as well as the design of the cognitive paradigm. These methodological limitations infl uence result interpretation hence hinder cross study comparison. Hemispheric study of memory using a pure working memory paradigm on native Chinese speakers, using a hemodynamic technique with high temporal resolution is thus mandatory. Objective: We aimed to investigate the feasibility of the functional transcranial Doppler sonography (fTCD) and 2-back task with alphabets in assessing the hemispheric lateralization of memory in healthy right-handed Chinese. Methods: Thirteen healthy right-handed Chinese subjects (7 males and 6 females, 19-22 years old) were included. Bilateral monitoring of the cerebral blood fl ow velocity (CFBV) changes in their left and right middle cerebral arteries (MCAs) was performed using fTCD during their performance of a 2-back working memory task with alphabets. Differences of CBFV change between left and right MCAs were analyzed, and the laterality index (LI) was determined. Results: Left lateralization was found in all subjects, with females performed better than males (p < 0.05). No difference in age, response time and LI between the male and female subjects could be observed (p > 0.05). A weak correlation was found between performance accuracy/response time and LI (r = 0.12). Conclusion: To the best of our knowledge, this is the fi rst report on the use of fTCD in memory function assessment in Chinese. The consistency of our results with previous studies demonstrates the feasibility as well as the potential application of the 2-back task with alphabets and fTCD, as a bedside assessment system of memory function in native Chinese speaking population. Neurology Asia 2012; 17(1) : 39 – 48 Address correspondence to: Winnie Wai-Ying Kam, Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW 2234 Australia, Phone: (612)97177241, Email: [email protected] INTRODUCTION Memory, especially working memory, plays an important role in human life. Working memory is responsible for short-term storage and online manipulation of information necessary for higher cognitive functions such as planning and problemsolving, with the prefrontal cortex as the primary executing region. Brain lesion in different neural regions exerts different degree of defi cits in brain function. Information on the hemispheric memory dominance is of particular importance for risk evaluation on memory disturbance/impairment prior to a resective brain surgery, or electrode positioning of an electroconvulsive therapy. A wide range of imaging tests such as the intracarotid amobarbital procedure (or termed as the Wada test) and functional magnetic resonance imaging (fMRI) have been applied in the investigation of hemispheric lateralization of various cognitive activities. Invasiveness, ionizing radiation, prolonged procedure in intracarotid amobarbital procedure; high cost, low temporal resolution and the contraindication of having MRI exam for subjects with metallic implants are the most infl uencing drawbacks in providing a holistic picture in hemispheric lateralization research with optimum economy and safety. Functional transcranial Doppler sonography (fTCD) is a more superior functional tool than Neurology Asia March 2012 40 intracarotid amobarbital procedure and fMRI in the context of hemispheric lateralization determination due to its low cost, high portability and non-invasiveness. fTCD applies similar principle as fMRI in hemispheric lateralization determination – the level of increase in cerebral blood fl ow velocity (CBFV) is directly related to the level of cerebral activation during an engagement of a cognitive task. It has been reported that the high temporal resolution of fTCD allows real-time bilateral monitoring of CBFV change during language and cognitive processing. Recent studies also demonstrated that fTCD and fMRI are highly correlated with the Wada test (gold standard) in the determination of cerebral lateralization. fTCD has been mainly applied in the quantifi cation of hemispheric perfusion differences in language. Only one recent study utilized fTCD in working memory hemispheric lateralization determination using alphabetic language speaking population. However, the successfulness of fTCD in working memory hemispheric lateralization assessment might be affected by the possible hemodynamic difference between the alphabetic and logographic language speaking populations. Thus, a wider application of fTCD in working memory lateralization assessment awaits the feasibility investigation using subjects from a logographic language speaking population e.g. Chinese. Cognitive style adopted during the mental task poses a greater effect in determining the hemispheric lateralization than the type of stimulus provided. Nystron’s investigation found a greater activation for region expected for verbal memory in an object working memory task. They suggested that subjects may apply verbal approach in naming object stimuli and practice subvocal rehearsal for memorization, thus activating verbal memory area. In a recent study which applied fTCD in the assessment of memory function on Italians, subjects were requested to encode and immediate recall of a short written text describing a room. Left hemispheric dominance was found in the subjects, however, the authors pointed out that processing of this verbal material could involve visuospatial imagery resources. Therefore, the appropriateness of the cognitive task is crucial for a pure memory function examination. In this study, we aimed to investigate the feasibility of fTCD and 2-back working memory task with alphabets in assessing the laterality of memory processing in healthy right-handed Chinese. METHODS