Functional MR imaging in Alzheimer's disease during memory encoding

Abstract

Background and purpose: We applied functional MR imaging with a learning task in healthy elderly volunteers and in patients with Alzheimer's disease to study brain activation during memory performance. The purpose was to determine the feasibility of functional MR imaging during a learning task in healthy elderly volunteers and in patients with Alzheimer's disease and to test our hypothesis that brain activation is decreased in the medial temporal lobe (MTL) memory system in patients with Alzheimer's disease compared with control volunteers.

Methods: In 12 patients with mild to moderate forms of Alzheimer's disease and 10 elderly control volunteers, activation of the MTL memory system was studied. We used two learning tasks that required the encoding of new information into memory. After the functional MR imaging experiment, participants were tested for recognition of the encoded objects.

Results: In the elderly control volunteers, activation during memory encoding was observed in medial and lateral temporal lobe structures (fusiform, parietal and occipital parts, and hippocampal formation) and in the frontal cortex, as reported previously in studies of young control volunteers. Focusing on the MTL, we observed that activation was significantly decreased in patients with Alzheimer's disease compared with control volunteers in the left hippocampus and parahippocampal gyrus bilaterally during the first encoding task but not during the second (P < .05, uncorrected).

Conclusion: Functional MR imaging with a learning task seems feasible in elderly volunteers and in patients with Alzheimer's disease. The measured functional signal decrease in MTL areas warrants further exploration of the (early) diagnostic usefulness of functional MR imaging in cases of Alzheimer's disease and other dementias.

fig 1.

Projection of average brain activation during encoding of color pictures in sagittal, coronal, and transverse directions in the control group and in the patients. A, Control group (n = 10, left in picture is left in brain). A one-sample t test random effects analysis (P < .001; uncorrected; minimal cluster size, 108 mm³) was applied. Significant activation is observed in the occipital cortex, fusiform gyri, left parahippocampal gyrus, parietal lobe, and left inferior frontal gyrus. B, Patients (n = 11). The main effect of signal increase is seen in the occipital cortex, right parahippocampal gyrus, fusiform gyrus, and cerebellum.

fig 2.

Sagittal, coronal, and transverse sections showing a significant increase in brain activation in control volunteers compared with patients in the left hippocampus and parahippocampal gyrus (black areas) during the first task, after application of the region of interest analysis (P < .05, uncorrected). The same effect is seen in the right parahippocampal gyrus (not shown). Activation is projected on the average brain of the 10 control volunteers (3D gradient-echo, T1-weighted sequence with parameters 15/7/1). Left in the figure is left in the brain

fig 3.

Projection of average brain activation during encoding of line drawings in sagittal, coronal, and transverse directions in the control group and in patients. A, Control group (n = 10, left in the figure is left in the brain). A one-sample t test random effects analysis (P < .001; uncorrected; minimal cluster size, 108 mm³) was applied. Significant activation is observed in the cerebellum, occipital cortex, parietal cortex, inferior frontal gyrus, and left parahippocampal gyrus. B, Patients (n = 8). The main effect of signal increase is seen in the occipital and parietal cortex, right precentral gyrus, left insula, left middle frontal gyrus, and cingulate sulcus.