1. ¹Department of Neurology, Democritus University of Thrace, University Hospital of Alexandroupolis, Alexandroupolis, Greece
2. ²Second Department of Neurology, AHEPA Hospital, Aristotle University, Thessaloniki, Greece
3. ³Department of Neurology, Henry Ford Health System, Detroit, Michigan, USA
4. ⁴Department of Medical Statistics, Democritus University of Thrace, Thrace, Greece

Correspondence: Dr KM Vadikolias, Department of Neurology, Democritus University of Thrace, University Hospital, Alexandroupolis, Greece. E-mails: kvadikol@med.duth.gr or vadikosm@yahoo.com

Received 16 November 2006; Revised 30 January 2007; Accepted 15 February 2007; Published online 11 April 2007.

Abstract

Functional transcranial Doppler (fTCD) has been used for the identification of cerebral hemispheric dominance in various cognitive tasks. In our study, we have used fTCD with the aim to compare blood flow patterns in the hemispheres not only during the task activation periods but also in the post-stimulus phase. Normal volunteers, 25 right and 25 left-handed, were included. Mean flow velocities (FVs) in the bilateral middle cerebral arteries were recorded during the performance of six cognitive tasks and during the intervals between tasks. The lateralization index (LI) was calculated separately for each test (LI1-6), on the basis of the percent change of blood FV from baseline. To estimate flow fluctuations, a novel index, the LI-variability, was also calculated using a formula constituted by the minimum and maximum mean values recorded at specific time intervals during the entire procedure. Laterization indices, LI-3 and LI-4, corresponding to word generation and reading aloud tasks, produced the highest degree of activation. A perfect agreement (Cohen's =1.000, P<0.001) was observed among LI-3, LI-4, and LI-V. The repetition of recordings gave excellent test–retest reliability in 10 randomly selected participants. Our results suggest that the hemisphere that is characterized as dominant by fTCD maintains a more stable flow pattern during the performance of successive cognitive tasks. Although it could not be considered as a clinically useful tool as yet, this observation introduces a novel parameter such as the stability of blood flow over time, which could potentially provide insight in the study of cerebral functions.