Exploratory behaviors during learning determine what is studied and when, helping to optimize subsequent memory performance. We manipulated how much control subjects had over the position of a moving window through which they studied objects and their locations, in order to elucidate the cognitive and neural determinants of exploratory behaviors. Our behavioral, neuropsychological, and neuroimaging data indicate volitional control benefits memory performance, and is linked to a brain network centered on the hippocampus. Increases in correlated activity between the hippocampus and other areas were associated with specific aspects of memory, suggesting that volitional control optimizes interactions among specialized neural systems via the hippocampus. Memory is therefore an active process intrinsically linked to behavior. Furthermore, brain structures typically seen as passive participants in memory encoding (e.g., the hippocampus) are actually part of an active network that controls behavior dynamically as it unfolds.

Declarative memory permits an organism to recognize stimuli that have been previously encountered, discriminating them from those that are novel. One basis for recognition is item memory strength, which may support the perception of stimulus familiarity. Though the medial temporal lobes are known to be critical for declarative memory, at present the neural mechanisms supporting perceived differences in memory strength remain poorly specified. Here, functional MRI (fMRI) and anatomically constrained magnetoencephalography (MEG) indexed correlates of graded memory strength in the human brain, focusing on medial temporal cortex. fMRI revealed a decrease in medial temporal cortical activation that tracked parametric levels of perceived memory strength. Anatomically constrained MEG current estimates revealed that strength-dependent signal reductions onset within 150-300 ms. Memory strength appears to be rapidly signaled by medial temporal cortex through repetition suppression (activation reductions), providing a basis for the subjective perception of stimulus familiarity or novelty.

Effective exploratory behaviors involve continuous updating of sensory sampling to optimize the efficacy of information gathering. Despite some work on this issue in animals, little information exists regarding the cognitive or neural mechanisms for this sort of behavioral optimization in humans. Here we examined a visual exploration phenomenon that occurred when human subjects studying an array of objects spontaneously looked "backward" in their scanning paths to view recently seen objects again. This "spontaneous revisitation" of recently viewed objects was associated with enhanced hippocampal activity and superior subsequent memory performance in healthy participants, but occurred only rarely in amnesic patients with severe damage to the hippocampus. These findings demonstrate the necessity of the hippocampus not just in the aspects of long-term memory with which it has been associated previously, but also in the short-term adaptive control of behavior. Functional neuroimaging showed hippocampal engagement occurring in conjunction with frontocerebellar circuits, thereby revealing some of the larger brain circuitry essential for the strategic deployment of information-seeking behaviors that optimize learning.amnesia | prefrontal cortex | vicarious trial-and-error behavior O ne of the hallmarks of higher cognitive functioning is the ability to flexibly tailor behaviors to current situational demands. An example comes from the purposeful way animals explore the environment, effectively sampling the particular information most critical for learning and later memory. A number of investigators have emphasized the critical role in such behaviors of memory systems (1, 2) and strategic/executive control systems (3, 4). Some theorizing about exploratory behaviors has emphasized the potential importance of constant iteration between perception and action (5, 6) or between prediction and verification (7-9). However, little is known, at least in humans, about precisely how processing in neural systems leads to the optimization of exploratory behaviors and how the behaviors, in turn, affect processing in these systems as learning occurs. This is partially because contemporary research often involves exposing individuals to some information and relating brain activity to the ability to later recall or recognize aspects of the original learning event (10). Findings therefore primarily concern processes closely allied with introspective reports rather than the processes by which memory signals are used by the organism in the moment-tomoment guidance of dynamic behavior.Connections between brain activity and ongoing behavior are generally better understood in animals, in which the assaying of active behaviors is a necessity for studying learning and memory.* For the work reported here, one notable example is a phenomenon in rodents described by Muenzinger (13) and Tolman (7-9) that seems to relate memory processing and exploratory behavior. When learning to discriminate between two stimuli based on one item's selective associa...

ABSTRACT-The imperfect nature of memory is highlighted by the regularity with which people fail to remember, or worse, remember something that never happened. We investigated the formation of a particular type of erroneous memory by monitoring brain activity using functional magnetic resonance imaging during the presentation of words and photos. Participants generated a visual image of a common object in response to each word. Subsequently, they sometimes claimed to have seen photos of specific objects they had imagined but not actually seen. In precuneus and inferior parietal regions of the cerebral cortex, activations in response to words were greater when participants subsequently claimed to have seen the corresponding object than when a false memory for that object was not subsequently produced. These findings indicate that brain activity reflecting the engagement of visual imagery can lead to falsely remembering something that was only imagined.

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