Prefrontal involvement in source memory: an electrophysiological investigation of accounts concerning confidence and accuracy

Brain regions and functional interactions supporting early word recognition in the face of input variability

Perception and cognition in infants have been traditionally investigated using habituation paradigms, assuming that babies' memories in laboratory contexts are best constructed after numerous repetitions of the very same stimulus in the absence of interference. A crucial, yet open, question regards how babies deal with stimuli experienced in a fashion similar to everyday learning situations-namely, in the presence of interfering stimuli. To address this question, we used functional near-infrared spectroscopy to test 40 healthy newborns on their ability to encode words presented in concomitance with other words. The results evidenced a habituation-like hemodynamic response during encoding in the left-frontal region, which was associated with a progressive decrement of the functional connections between this region and the left-temporal, right-temporal, and right-parietal regions. In a recognition test phase, a characteristic neural signature of recognition recruited first the right-frontal region and subsequently the right-parietal ones. Connections originating from the right-temporal regions to these areas emerged when newborns listened to the familiar word in the test phase. These findings suggest a neural specialization at birth characterized by the lateralization of memory functions: the interplay between temporal and left-frontal regions during encoding and between temporo-parietal and right-frontal regions during recognition of speech sounds. Most critically, the results show that newborns are capable of retaining the sound of specific words despite hearing other stimuli during encoding. Thus, habituation designs that include various items may be as effective for studying early memory as repeated presentation of a single word.

How Negative Social Bias Affects Memory for Faces: An Electrical Neuroimaging Study

During social interactions, we make inferences about people’s personal characteristics based on their appearance. These inferences form a potential prejudice that can positively or negatively bias our interaction with them. Not much is known about the effects of negative bias on face perception and the ability to recognize people faces. This ability was investigated by recording event-related potentials (ERPs) from 128 sites in 16 volunteers. In the first session (encoding), they viewed 200 faces associated with a short fictional story that described anecdotal positive or negative characteristics about each person. In the second session (recognition), they underwent an old/new memory test, in which they had to distinguish 100 new faces from the previously shown faces. ERP data relative to the encoding phase showed a larger anterior negativity in response to negatively (vs. positively) biased faces, indicating an additional processing of faces with unpleasant social traits. In the recognition task, ERPs recorded in response to new faces elicited a larger FN400 than to old faces, and to positive than negative faces. Additionally, old faces elicited a larger Old-New parietal response than new faces, in the form of an enlarged late positive (LPC) component. An inverse solution SwLORETA (450–550 ms) indicated that remembering old faces was associated with the activation of right superior frontal gyrus (SFG), left medial temporal gyrus, and right fusiform gyrus. Only negatively connoted faces strongly activated the limbic and parahippocampal areas and the left SFG. A dissociation was found between familiarity (modulated by negative bias) and recollection (distinguishing old from new faces).

Testing the domain-general nature of monitoring in the spatial and verbal cognitive domains

While it is well-established that monitoring the environment for the occurrence of relevant events represents a key executive function, it is still unclear whether such a function is mediated by domain-general or domain-specific mechanisms. We investigated this issue by combining event-related potentials (ERPs) with a behavioral paradigm in which monitoring processes (non-monitoring vs. monitoring) and cognitive domains (spatial vs. verbal) were orthogonally manipulated in the same group of participants. They had to categorize 3-dimensional visually presented words on the basis of either spatial or verbal rules. In monitoring blocks, they additionally had to check whether the word displayed a specific spatial configuration or whether it contained a certain consonant. The behavioral results showed slower responses for both spatial and verbal monitoring trials compared to non-monitoring trials. The ERP results revealed that monitoring did not interact with domain, thus suggesting the involvement of common underlying mechanisms. Specifically, monitoring acted on low-level perceptual processes (as expressed by an enhanced visual N1 wave and a sustained posterior negativity for monitoring trials) and on higher-level cognitive processes (involving larger positive modulations by monitoring trials over frontal and parietal scalp regions). The source reconstruction analysis of the ERP data confirmed that monitoring was associated with increased activity in visual areas and in right prefrontal and parietal regions (i.e., superior and inferior frontal gyri and posterior parietal cortex), which previous studies have linked to spatial and temporal monitoring. Our findings extend this research by supporting the domain-general nature of monitoring in the spatial and verbal domains.

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Previous studies suggest that monitoring relies on domain-general mechanisms.

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We combined EEG with a novel experimental design to directly test this hypothesis.

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Spatial and verbal non-monitoring and monitoring tasks were performed.

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Results confirmed the domain-general nature of monitoring.

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EEG source reconstruction showed the involvement of common right fronto-parietal areas.

An Electrophysiological Dissociation between Orbitofrontal Reality Filtering and Context Source Monitoring

Memory influences behavior in multiple ways. One important aspect is to remember in what precise context in the past a piece of information was acquired (context source monitoring). Another important aspect is to sense whether an upcoming thought, composed of fragments of memories, refers to present reality and can be acted upon (orbitofrontal reality filtering). Whether these memory control processes share common underlying mechanisms is unknown. Failures of both have been held accountable for false memories, including confabulation. Electrophysiological and imaging studies suggest a dissociation but used very different paradigms. In this study, we juxtaposed the requirements of context source monitoring and reality filtering within a unique continuous recognition task, which healthy participants performed while high-resolution evoked potentials were recorded. The mechanisms dissociated both behaviorally and electrophysiologically: Reality filtering induced a frontal positivity, absence of a specific electrocortical configuration, and posterior medial orbitofrontal activity at 200–300 msec. Context source monitoring had no electrophysiological expression in this early period. It was slower and less accurate than reality filtering and induced a prolonged positive potential over frontal leads starting at 400 msec. The study demonstrates a hitherto unrecognized separation between orbitofrontal reality filtering and source monitoring. Whereas deficient orbitofrontal reality filtering is associated with reality confusion in thinking, the behavioral correlates of deficient source monitoring should be verified with controlled experimental exploration.

Asymmetric hemispheric contribution to ERPs in associative memory indexes goal relevance and quantity of information

Explicit encoding requires humans to select the information relevant to their goals, yet not all irrelevant information is discarded. The present study addressed how different quantity and relevance of information modulate the electrophysiological activity during the encoding and retrieval phases of a recognition memory task. Subjects learned associations between two semantically unrelated pictures, and then performed a recognition judgment. After recognition, subjects were asked to recall the associated picture by using the recognized image as a cue. Cues yielded either high quantity of information (the cue evoked two associations, only one of them being relevant to the task), or low quantity of information (the cue evoked a single, relevant association). At encoding, a negative peak (400 ms) showed reduced negativity at left sites for the associative trials compared to the non-associative ones, while at right frontal sites the peak was more negative for goal-unrelated associations, compared to goal-related ones. Late right negativity during the test phase (800-1000 ms) discriminated hits followed either by correct or by no recall, but only when the cue evoked multiple associations. Frontal electrophysiological asymmetry at encoding was affected by the behavioral goal, i.e. activity reflected goal-related encoding on the left and goal-unrelated encoding on the right. The late right effect at retrieval suggests a link between this activity during encoding and the evaluation of the higher quantity of information in light of the behavioral goal during retrieval. Overall, the results indicate that different mechanisms and/or neuronal populations are involved in goal-related versus goal-unrelated association.

Neural correlates of source memory retrieval in young, middle-aged and elderly adults

Event-related potentials (ERPs) were recorded in young (21-27 years old), middle-aged (50-57 years old) and older adults (70-77 years old) to determine whether the decline in source memory that occurs with advancing age coincides with contemporaneous neurophysiological changes. Source memory for the spatial location (quadrant on the screen) of images presented during encoding was examined. The images were shown in the center of the screen during the retrieval task. Retrieval success for source information was characterized by different scalp topographies at frontal electrode sites in young adults relative to middle-aged and older adults. The right frontal effect during unsuccessful retrieval attempts showed amplitude and latency differences across age groups and was related to the ability to discriminate between old and new images only in young adults. These results suggest that the neural correlates of the retrieval success and attempt were affected by age and these effects were present by middle-age.

Routes to the past: neural substrates of direct and generative autobiographical memory retrieval

Models of autobiographical memory propose two routes to retrieval depending on cue specificity. When available cues are specific and personally-relevant, a memory can be directly accessed. However, when available cues are generic, one must engage a generative retrieval process to produce more specific cues to successfully access a relevant memory. The current study sought to characterize the neural bases of these retrieval processes. During functional magnetic resonance imaging (fMRI), participants were shown personally-relevant cues to elicit direct retrieval, or generic cues (nouns) to elicit generative retrieval. We used spatiotemporal partial least squares to characterize the spatial and temporal characteristics of the networks associated with direct and generative retrieval. Both retrieval tasks engaged regions comprising the autobiographical retrieval network, including hippocampus, and medial prefrontal and parietal cortices. However, some key neural differences emerged. Generative retrieval differentially recruited lateral prefrontal and temporal regions early on during the retrieval process, likely supporting the strategic search operations and initial recovery of generic autobiographical information. However, many regions were activated more strongly during direct versus generative retrieval, even when we time-locked the analysis to the successful recovery of events in both conditions. This result suggests that there may be fundamental differences between memories that are accessed directly and those that are recovered via the iterative search and retrieval process that characterizes generative retrieval.

Different structural correlates for verbal memory impairment in temporal lobe epilepsy with and without mesial temporal lobe sclerosis

OBJECTIVES

Memory impairment is one of the most prominent cognitive deficits in temporal lobe epilepsy (TLE). The overall goal of this study was to explore the contribution of cortical and hippocampal (subfield) damage to impairment of auditory immediate recall (AIMrecall), auditory delayed recall (ADMrecall), and auditory delayed recognition (ADMrecog) of the Wechsler Memory Scale III (WMS-III) in TLE with (TLE-MTS) and without hippocampal sclerosis (TLE-no). It was hypothesized that volume loss in different subfields determines memory impairment in TLE-MTS and temporal neocortical thinning in TLE-no.

METHODS

T1 whole brain and T2-weighted hippocampal magnetic resonance imaging and WMS-III were acquired in 22 controls, 18 TLE-MTS, and 25 TLE-no. Hippocampal subfields were determined on the T2 image. Free surfer was used to obtain cortical thickness averages of temporal, frontal, and parietal cortical regions of interest (ROI). MANOVA and stepwise regression analysis were used to identify hippocampal subfields and cortical ROI significantly contributing to AIMrecall, ADMrecall, and ADMrecog.

RESULTS

In TLE-MTS, AIMrecall was associated with cornu ammonis 3 (CA3) and dentate (CA3&DG) and pars opercularis, ADMrecall with CA1 and pars triangularis, and ADMrecog with CA1. In TLE-no, AIMrecall was associated with CA3&DG and fusiform gyrus (FUSI), and ADMrecall and ADMrecog were associated with FUSI.

CONCLUSION

The study provided the evidence for different structural correlates of the verbal memory impairment in TLE-MTS and TLE-no. In TLE-MTS, the memory impairment was mainly associated by subfield-specific hippocampal and inferior frontal cortical damage. In TLE-no, the impairment was associated by mesial-temporal cortical and to a lesser degree hippocampal damage.

Synchronous retinotopic frontal-temporal activity during long-term memory for spatial location

Early visual areas in occipital cortex are known to be retinotopic. Recently, retinotopic maps have been reported in frontal and parietal cortex during spatial attention and working memory. The present event-related potential (ERP) and functional magnetic resonance imaging (fMRI) study determined whether spatial long-term memory was associated with retinotopic activity in frontal and parietal regions, and assessed whether retinotopic activity in these higher level control regions was synchronous with retinotopic activity in lower level visual sensory regions. During encoding, abstract shapes were presented to the left or right of fixation. During retrieval, old and new shapes were presented at fixation and participants classified each shape as old and previously on the "left", old and previously on the "right", or "new". Retinotopic effects were manifested by accurate memory for items previously presented on the left producing activity in the right hemisphere and accurate memory for items previously presented on the right producing activity in the left hemisphere. Retinotopic ERP activity was observed in frontal regions and visual sensory (occipital and temporal) regions. In frontal cortex, retinotopic fMRI activity was localized to the frontal eye fields. There were no significant ERP or fMRI retinotopic memory effects in parietal regions. The present long-term memory retinotopic effects complement previous spatial attention and working memory findings (and suggest retinotopic activity in parietal cortex may require an external peripheral stimulus). Furthermore, ERP cross-correlogram analysis revealed that retinotopic activations in frontal and temporal regions were synchronous, indicating that these regions interact during retrieval of spatial information.

When Time Shapes Behavior: fMRI Evidence of Brain Correlates of Temporal Monitoring

Time processing may shape behavior in several ways, although the underlying neural correlates are still poorly understood. When preparatory intervals between stimuli vary randomly in a block, for instance, responses are faster as the interval gets longer. This effect, known as variable foreperiod (FP) effect, has been attributed to a process monitoring the conditional probability of stimulus occurrence as the interval increases. Previous evidence points to the right dorsolateral prefrontal cortex (DLPFC) as a possible node for this time-monitoring process. The present study addresses this hypothesis with functional magnetic resonance imaging (fMRI). Block-design fMRI was used on 14 young participants while they performed a visual discrimination task with fixed and variable preparatory intervals (FPs) of 1 and 3 sec. In the variable versus fixed FP contrast, the right DLPFC and a visual area were more activated in the subgroup of participants who showed a reliable variable FP effect than in another subgroup who did not show that effect. Only the activation in the right DLPFC was supported by a significant interaction between FP condition (variable vs. fixed) and group. This finding may reflect possible differences in the strategy adopted by the two subgroups of participants while performing the task. Although results suggest that many brain areas may be involved in preparation over time, the role of the right DLPFC is critical to observe the strategically mediated behavioral effects in the variable FP paradigm.

Rapid retinotopic reactivation during spatial memory

Memories are thought to be constructed from features processed in different cortical regions. However, it is unknown how the retrieval process unfolds over time. The present investigation aimed to address this issue by combining evidence from event-related potentials (ERPs) and functional magnetic resonance imaging (fMRI). During study, abstract shapes were presented to the left or right of fixation and participants were instructed to remember each shape and its spatial location. At test, studied (old) and new shapes were presented at fixation and participants classified each shape as old and on the "left", old and on the "right", or "new". Accurate memory for items previously presented on the left or right produced fMRI activity in the right or left extrastriate cortex (BA18), respectively. ERP results revealed these retinotopic memory effects occurred within 100-250 ms after stimulus onset indicating memory construction can occur very rapidly.

Prefrontal cortex involvement in the event-based prospective memory: evidence from patients with lesions in the prefrontal cortex

PRIMARY OBJECTIVE

The aim of the present study was to investigate the event-based prospective memory (EBPM) and time-based prospective memory (TBPM) in patients with lesion in prefrontal cortex (PFC) and test the hypothesis that the prefrontal cortex is involved in the prospective memory (PM) network.

RESEARCH DESIGN

The performance of patients with lesion in PFC (n = 30) was compared with that of a demographically matched control group (n = 30).

METHODS AND PROCEDURES

A neuropsychological battery of tests including EBPM and TBPM tasks were administered to both groups.

MAIN OUTCOME AND RESULTS

The group with lesion in PFC were significantly impaired in EBPM, but insignificantly impaired in TBPM tasks. There was no difference in performance of EBPM and TBPM tasks between the patients with lesion in the left and the right PFC.

CONCLUSIONS

These results suggest that the patients with lesion in PFC were impaired in EBPM, but not in TBPM, implying that EBPM and TBPM may have different neural substrates. It is possible that PFC is more selectively involved in EBPM, but less in TBPM.