PubMed · 8275914
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L Laplante, J Everett. [Hypofrontality and schizophrenia].. https://pubmed.ncbi.nlm.nih.gov/8275914/
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The notion of overlap between encoding and retrieval processes is central in cognitive theories of episodic memory, but to date most functional neuroimaging studies have emphasized differences between these processes. In the present study, overlap between encoding and retrieval processes was investigated by analyzing data from a positron emission tomography (PET) study of encoding and retrieval of different kinds of event information. Using a conjunction analysis, we specifically aimed at identifying overlap in activation patterns for encoding and retrieval of three classes of event information: item, temporal, and spatial. It was found that both encoding and retrieval of spatial information activated posterior parietal areas bilaterally. In addition, item encoding and retrieval were associated with increased activity in the right temporal pole, and temporal encoding and retrieval with left inferior frontal and left inferior temporal regions. These findings suggest that when specific episodic information is retrieved from memory, regions involved in encoding of the same information are engaged.
Previous studies have shown differential responses in the fusiform and lingual gyri during reading and suggested that the former is engaged in processing local features of visual stimuli and the latter is engaged in global shape processing. We used positron emission tomography in order to investigate how these regions are modulated by two common variables in reading: word length (three, six and nine letters) and perceptive similarity to the background (high and low contrast). Increasing both word length and visual contrast had a positive monotonic effect on activation in the bilateral fusiform. However, in the lingual gyrus, activation increased with increasing word length but decreased with increasing contrast. On the basis of previous studies, we suggest that (i) increasing word length increases the demands on both local feature and global shape processing, but (ii) increasing visual contrast increases the demands on local feature processing while decreasing the demands on global shape processing.
Although there are elegants maps of the human brain that reveal differences in cellular architecture between different cortical regions, there is not much information about how corresponding cortical regions differ between the left and right hemispheres. As Gazzaniga explains in his Perspective, new results reveal the surprising finding of asymmetry in area 22 (which is important for language processing) of the left and right hemisphere (Galuske et al.). Clusters of neurons in area 22 of the left hemisphere are spaced farther apart and have longer axons cabling them together than neuronal clusters in area 22 of the right hemisphere.