Caffeine attenuates practice effects in word stem completion as measured by fMRI BOLD signal

Abstract

Caffeine ingestion results in increased brain cell metabolism (Nehlig et al. [1992] Brain Res Brain Res Rev 17:139-170) and decreased cerebral blood flow (Field et al. [2003] Radiology 227:129-135; Mulderink et al. [2002] Neuroimage 15:37-44). The current study investigated the effect of caffeine in a word stem completion task using only novel word stems (no repeated stimuli). Resting perfusion was measured with arterial spin labeled perfusion MRI, along with blood oxygenation level-dependent (BOLD) signal before and after ingestion of regular coffee, decaffeinated coffee, and water. Based on previous research (Laurienti et al. [2002] Neuroimage 17:751-757; Mulderink et al. [2002] Neuroimage 15:37-44), we hypothesized that caffeine would result in increased BOLD signal intensity and extent of BOLD activation. As expected, caffeine resulted in a significant decrease in cerebral perfusion. However, both the control and caffeine groups showed an increase in BOLD signal amplitude across two sets of novel word stems. Additionally, the control group showed a 50% reduction in the extent of BOLD activation, while the caffeine group showed no change in activation extent. Neither group showed changes in BOLD baseline signal over time, which had been suggested to mediate caffeine-related BOLD signal changes. The results suggest that caffeine may attenuate general task practice effects that have been described in recent functional MRI studies of word stem completion (Buckner et al. [2000] Brain 123:620-640).

Figure 1

Perfusion before (PRE‐BEV) and after (POST‐BEV) beverage ingestion. Perfusion change across the whole brain is shown on the left. The bars represent a change in signal between images collected with and without selective inversion (ΔS). It was of particular interest whether perfusion changed from PRE‐BEV to POST‐BEV in voxels where BOLD signal amplitude was assessed (shown on the right). We used the PRE‐BEV BOLD mask and applied it to the PRE‐BEV perfusion data and the POST‐BEV perfusion data to assess change in perfusion. In both analyses the caffeine group showed a significant decrease in perfusion following beverage ingestion. Error bars are SEM.

Figure 2

Voxel activation before (PRE‐BEV) and after (POST‐BEV) beverage ingestion. Voxels that met statistical significance for activation were counted in each participant PRE‐BEV and POST‐BEV. A group average was calculated PRE‐BEV and POST‐BEV. The control group showed a significant decrease in the number of active voxels from PRE‐BEV to POST‐BEV, while the caffeine group showed virtually no change in the number of active voxels from PRE to POST. Error bars are SEM.

Figure 3

Signal amplitude before (PRE‐BEV) and after (POST‐BEV) beverage ingestion. Signal amplitude was calculated for each participant by averaging the peak intensity values at 4, 6, and 8 s poststimulus onset for all significant voxels PRE‐BEV and POST‐BEV (shown on the left). Both the caffeine group and the control group showed an increase in signal amplitude during the second word stem completion task (POST‐BEV). Signal amplitude was also assessed in five voxels that met statistical significance for activation both PRE‐BEV and POST‐BEV (shown on the right). The pattern is identical to that found for all significantly active voxels in the brain. Error bars are SEM.