SHORT-TERM AND LONG-TERM VERBAL MEMORY - A POSITRON EMISSION TOMOGRAPHY STUDY

Short-term and long-term retention of err perimentally presented words were compared in a sample of 33 healthy normal volunteers by the [O-1 5]H2O method with positron emission tomography (PET). The design inclu ded three conditions. For the long-term condition, subjects thoroughly studied 18 words 1 week before the PET study. For the short-term cond ition, subjects were shown another set of 18 words 60 sec before imagi ng, with instructions to remember them. For the baseline condition, su btracted from the two memory conditions, subjects read a third set of words that they had not previously seen in the experiment. Similar reg ions were activated in both short-term and long-term conditions: large right frontal areas, biparietal areas, and the left cerebellum. In ad dition, the short-term condition also activated a relatively large reg ion in the left prefrontal region. These complex distributed circuits appear to represent the neural substrates for aspects of memory such a s encoding, retrieval, and storage. They indicate that circuitry invol ved in episodic memory has much larger cortical and cerebellar compone nts than has been emphasized in earlier lesion studies.