Late onset of anterior prefrontal activity during true and false recognition: an event-related fMRI study

The cognitive neuroscience of constructive memory

Numerous empirical and theoretical observations point to the constructive nature of human memory. This paper reviews contemporary research pertaining to two major types of memory distortions that illustrate such constructive processes: (a) false recognition and (b) intrusions and confabulations. A general integrative framework that outlines the types of problems that the human memory system must solve in order to produce mainly accurate representations of past experience is first described. This constructive memory framework (CMF) emphasizes processes that operate at encoding (initially binding distributed features of an episode together as a coherent trace; ensuring sufficient pattern separation of similar episodes) and also at retrieval (formation of a sufficiently focused retrieval description with which to query memory; postretrieval monitoring and verification). The framework is applied to findings from four different areas of research: cognitive studies of young adults, neuropsychological investigations of brain-damaged patients, neuroimaging studies, and studies of cognitive aging.

Functional-anatomic correlates of object priming in humans revealed by rapid presentation event-related fMRI

Human functional-anatomic correlates of object repetition were explored in a cohort of 20 subjects using fMRI. Subjects performed an object classification task where the target objects were either novel or repeated. Objects appeared rapidly, one every 2 s, in a randomly intermixed task design similar to traditional behavioral, event-related potential (ERP), and single-unit physiological studies. Recently developed event-related fMRI methods were used to analyze the data. Clear effects of repetition were observed. Brain areas in midlevels of the processing hierarchy, including extrastriate visual cortex extending into inferotemporal cortex and left dorsal prefrontal cortex, showed reductions in the amount of activation after repetition. By contrast, early visual areas and output motor areas were activated equally by both novel and repeated objects and did not show effects of repetition, suggesting that the observed correlates of repetition were anatomically selective. We discuss these findings in relation to previous positron emission tomography (PET) and fMRI studies of item repetition and single-unit physiological studies; we also address the broad impact that rapid event-related fMRI is likely to have on functional neuroimaging.

Neuroanatomical correlates of implicit and explicit memory for structurally possible and impossible visual objects

Implicit memory refers to nonconscious retrieval of past experience demonstrated by facilitation in test performance on tasks that do not require intentional recollection of previous experiences. Explicit memory, in contrast, refers to the conscious retrieval of prior information, as demonstrated during standard recall and recognition tasks. In this experiment, positron emission tomographic (PET) measurements of regional cerebral blood flow (CBF), a marker of local neuronal activity, were used to identify and contrast brain regions that participate in the perception, implicit memory, and explicit memory for structurally possible and impossible visual objects. Ten CBF images were acquired in 16 normal women as they made possible/impossible and old/new recognition decisions about previously studied (old) and nonstudied (new) structurally possible and impossible objects. As reported previously, object decisions for familiar possible objects were associated with increased CBF in the vicinity of the left inferior temporal and fusiform gyri and recognition memory for familiar possible objects was associated with increased CBF in the vicinity of the right hippocampus. In this report, we provide more extensive analyses of the roles of the inferior temporal cortex, the hippocampus, the parahippocampus, and the pulvinar in encoding and retrieval operations. Additionally, patterns of CBF increases and decreases provide information regarding the neural structures involved in implicit and explicit memory.