Brain Activity and Blood flow Velocity Changes: A Transcranial Doppler Study

Abstract

Seventy volunteers with no sign of cerebral vascular disease performed two series of 6 cognitive tasks, 3 of which are assumed to be processed predominantly by the left and 3 by the right hemisphere. During the tasks, blood flow velocity changes in the middle cerebral artery were recorded every 3 seconds by the transcranial Doppler method (TCD). All tasks increased blood flow velocities in both MCAs, but only the "right hemispheric" tasks resulted in a statistically significantly higher increase than the left MCA. The time course of velocity changes reflects the increase in blood flow caused by increased brain metabolism during brain activity. During stimulation of the right and/or left visual field, blood flow velocity changes were recorded in the P2-segment of the corresponding hemisphere. In 76 volunteers, the study was performed. The time course of velocity changes was similar to that in the MCA study. Velocity rose as a result of increasing complexity of the visual stimulus. The velocity changes are similar to blood flow increases reported in the literature and rose by as much 2 to 25%. Assuming that the diameter of the large branches of the circle of Willis does not change during mental activity, blood flow velocity changes reflect blood flow volume changes. With the TCD method the close relationship among brain activity, metabolism, and blood flow can be reliably investigated. The high spatial resolution enables information to be given about the onset of autoregulation.

Contributions to the Development of Objective Techniques for Presence Measurement in Virtual Environments by means of Brain Activity Analysis

“…This is an issue that has been previously studied with TCD, using experimental designs that included visual stimuli with different degrees of complexity [29,30,31,32,33,34,35]. In this case, a simple visual perception task was selected, similar to that used in the study from Aaslid [29].…”

“…It is important to note that the BFV absolute or relative variations that can be observed during cognitive tasks are studied in most functional TCD works. However, and although the high temporal resolution of TCD is one of the key advantages of this technique, the instantaneous temporal evolution of BFV signals in subjects performing cognitive tasks has only been analyzed in some of the functional studies [20], which have found a maximum peak in BFV between 4 [180] to 20 s [181] after the initiation of a cognitive task, with an average peak after 6-9 s [31,158,149].…”

“…For example, Harders et al [31] analyzed BFV responses to different mental tasks, with a specific analysis of visual cortex activity, studying BFV in the PCA. Different stimuli with increasing complexity were used (such as illumination, illumination of both visual fields or looking at 6 pictures).…”

“…Temporal evolution was also studied, and it was found that elderly subjects achieved the maximum variations later than young subjects and returned to repose values more slowly. In a study from Harders et al [31] they calculated the mean of the maximum BFV every three seconds, and the evolution during the performance of different visual tasks was analyzed. It was found a maximum after 18 s, and a decrease 5 s after finishing the task.…”

“…As long as the neurovascular coupling occurs a few seconds after the beginning of a mental task [31,180,158,149,181] and velocity remains relatively constant while the activity is maintained, only a section of the period (both in the free navigation condition and the automatic navigation condition) was included in the analysis. This procedure can contribute to avoid BFV variations caused by factors different to the VE exposure (for example, a possible fatigue effect).…”