<P> According to neuroimaging data, PET studies on recall and recognition have consistently found increases in regional cerebral blood flow (RCBF) in the following six brain regions: (1) the prefrontal cortex, particularly on the right hemisphere; (2) the hippocampal and parahippocampal regions of the medial temporal lobe; (3) the anterior cingulate cortex; (4) the posterior midline area that includes posterior cingulate, retrosplenial (see retrosplenial region), precuneus, and cuneus regions; (5) the inferior parietal cortex, especially on the right hemisphere; and (6) the cerebellum, particularly on the left . </P> <P> The specific role of each of the six main regions in episodic retrieval is still unclear, but some ideas have been suggested . The right prefrontal cortex has been related to retrieval attempt; the medial temporal lobes to conscious recollection; the anterior cingulate to response selection; the posterior midline region to imagery; the inferior parietal to awareness of space; and the cerebellum to self - initiated retrieval . </P> <P> In recent research, a group of subjects was faced with remembering a list of items and then measured when trying to recall said items . The evoked potentials and hemodynamic activity measured during encoding were found to exhibit reliable differences between subsequently recalled and not recalled items . This effect has been termed the subsequent memory effect (SME). This difference in these specific brain regions determines whether or not an item is recalled . A study by Fernandez et al. has shown that the differences that predict recall appear both as a negative deflection in the rhinal cortex of an event - related potential (ERP) 400 ms after stimulus exposure, and as a positive hippocampal ERP beginning 800 ms after stimulus onset . This means that recall only occurs if these two brain regions (rhinal cortex and hippocampus) are activated in synchrony . </P> <P> The effect of attention on memory recall has surprising results . It seems that the only time attention largely affects memory is during the encoding phase . During this phase, performing a parallel task can severely impair retrieval success . It is believed that this phase requires much attention to properly encode the information at hand, and thus a distractor task does not allow proper input and reduces the amount of information learned . </P>

The ability to recall the order in which events have occurred can be attributed to