Effect of schizophrenia on frontotemporal activity during word encoding and recognition: a PET cerebral blood flow study

Abstract

Objective: Neuropsychological studies have shown that deficits in verbal episodic memory in schizophrenia occur primarily during encoding and retrieval stages of information processing. The current study used positron emission tomography to examine the effect of schizophrenia on change in cerebral blood flow (CBF) during these memory stages.

Method: CBF was measured in 23 healthy comparison subjects and 23 patients with schizophrenia during four conditions: resting baseline, motor baseline, word encoding, and word recognition. The motor baseline was used as a reference that was subtracted from encoding and recognition conditions by using statistical parametric mapping.

Results: Patients' performance was similar to that of healthy comparison subjects. During word encoding, patients showed reduced activation of left prefrontal and superior temporal regions. Reduced left prefrontal activation in patients was also seen during word recognition, and additional differences were found in the left anterior cingulate, left mesial temporal lobe, and right thalamus. Although patients' performance was similar to that of healthy comparison subjects, left inferior prefrontal activation was associated with better performance only in the comparison subjects.

Conclusions: Left frontotemporal activation during episodic encoding and retrieval, which is associated with better recognition in healthy people, is disrupted in schizophrenia despite relatively intact recognition performance and right prefrontal function. This may reflect impaired strategic use of semantic information to organize encoding and facilitate retrieval.

Figures

FIGURE 1

Brain Imagesa Showing Differencesb Between 23 Healthy Comparison Subjects and 23 Patients With Schizophrenia in Change in Regional Cerebral Blood Flow Between Word Encoding and Baseline Motor Task a Statistical parametric maps are displayed on an axial 4-mm MRI standardized into Talairach space extending in the z direction from −28 to 56. Images are in neurological convention (left is left). Colored areas exceed an uncorrected p value of 0.005 with 50 or more contiguous voxels activated. b Values for comparison subjects minus values for patients. Maxima of activation differences noted in left inferior frontal gyrus, middle frontal gyrus, superior frontal gyrus, and left inferior temporal gyrus.

FIGURE 2

Brain Imagesa Showing Differencesb Between 23 Healthy Comparison Subjects and 23 Patients With Schizophrenia in Change in Regional Cerebral Blood Flow Between Word Recognition and Baseline Motor Task a Statistical parametric maps are displayed as in Figure 1. b Values for comparison subjects minus values for patients. Maxima of activation differences noted in left inferior frontal gyrus, middle frontal gyrus, left parahippocampal gyrus, left anterior cingulate, and right thalamus.

FIGURE 3

Brain Imagesa Showing Pearson Correlationsb Between Target Discriminability and Change in Regional Cerebral Blood Flow Between Word Encoding and Baseline Motor Task for 20 Healthy Comparison Subjects and 19 Patients With Schizophreniac a Statistical parametric maps are displayed as in Figure 1. b Colored areas exceed an r value of 0.60. c For comparison subjects, the largest correlation is noted in the left inferior frontal gyrus; for patients, the largest correlations are noted in the left inferior temporal gyrus, left inferior parietal gyrus, left superior frontal gyrus, and right middle frontal gyrus.

FIGURE 4

Brain Imagesa Showing Pearson Correlationsb Between Target Discriminability and Change in Regional Cerebral Blood Flow Between Word Recognition and Baseline Motor Task for 20 Healthy Comparison Subjects and 19 Patients With Schizophreniac a Statistical parametric maps are displayed as in Figure 1. b Colored areas exceed an r value of 0.60. c For comparison subjects, the largest correlation is noted in the left inferior frontal gyrus; for patients, the largest correlations are noted in left hemisphere motor and supplementary motor cortices.