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Jon S Simons

Publications and source records attributed to Jon S Simons.

18 recordsLinked to original sources
PubMed2006

Discriminating imagined from perceived information engages brain areas implicated in schizophrenia.

Some of the symptoms of schizophrenia may reflect a difficulty discriminating between information that was perceived from the outside world and information that was imagined. This study used fMRI to examine the brain regions associated with this reality monitoring ability in healthy volunteers, who recollected whether information had previously been perceived or imagined, or whether information had been presented on the left or right of a monitor screen. Recent studies have suggested that schizophrenia may be associated particularly with dysfunction in medial anterior prefrontal cortex, thalamus, and cerebellum. In our data, activation in all three of these regions of interest was significantly greater during recollection of whether stimuli had been perceived or imagined versus recollection of stimulus position. In addition, reduced prefrontal activation was associated with the same misattribution error that has been observed in schizophrenia. These results indicate a possible link between the brain areas implicated in schizophrenia and the regions supporting the ability to discriminate between perceived and imagined information.

Adult↗
PubMed2006

Differential components of prospective memory? Evidence from fMRI.

Two of the principal components of prospective memory (i.e., remembering to carry out delayed intentions) are recognizing the appropriate context to act ("cue identification") and remembering the action to be performed ("intention retrieval"). In this experiment, the demands on these components were manipulated while measuring brain activity using fMRI to explore whether the two components share a common neural basis. The results showed significant behavioral differences between the cue identification and intention retrieval conditions. However, a consistent pattern of hemodynamic changes was found in both prospective memory conditions in anterior prefrontal cortex (BA 10), with lateral BA 10 activation accompanied by medial BA 10 deactivation. These effects were more pronounced when demands on intention retrieval were high. This is consistent with the hypothesis that anterior prefrontal cortex (area 10) supports the biasing of attention between external events (e.g., identifying the cue amid distracting stimuli) and internal thought processes (i.e., maintaining the intention and remembering the intended actions). Together, the results suggest that whilst cue identification and intention retrieval may be behaviorally separable, they share at least some common neural basis in anterior prefrontal cortex.

Adolescent↗
PubMed2006

Differential functions of lateral and medial rostral prefrontal cortex (area 10) revealed by brain-behavior associations.

We analyzed the behavioral data from 104 neuroimaging studies using positron emission tomography or functional magnetic resonance imaging that reported activation peaks in rostral prefrontal cortex (PFC), approximating Brodmann's area 10. The distribution of absolute x coordinates of activation peaks (i.e., x coordinate regardless of hemisphere) differed significantly from a unimodal normal distribution, reflecting distinct clusters of activation in lateral and medial subregions. These 2 clusters were associated with different patterns of behavioral data. Lateral activations were associated with contrasts between experimental and control conditions where response times (RTs) were slower in the experimental condition. Medial activations were associated with contrasts where RTs were, if anything, faster in experimental than control conditions. These findings place important constraints on theories of rostral PFC functions.

Adult↗
PubMed2006

Performance-related activity in medial rostral prefrontal cortex (area 10) during low-demand tasks.

Neuroimaging studies have frequently observed relatively high activity in medial rostral prefrontal cortex (PFC) during rest or baseline conditions. Some accounts have attributed this high activity to the occurrence of unconstrained stimulus-independent and task-unrelated thought processes during baseline conditions. Here, the authors investigated the alternative possibility that medial rostral PFC supports attention toward the external environment during low-demand conditions. Participants performed a baseline simple reaction time (RT) task, along with 3 other tasks that differed in the requirement to attend to external stimuli versus stimulus-independent thought. Medial rostral PFC activation was observed in the baseline task and in a condition requiring strong engagement with external stimuli, relative to 2 conditions with a greater requirement for stimulus-independent thought. An important finding was that activity in this region was associated with faster RTs in the baseline task, ruling out an explanation in terms of task-unrelated thought processes during this condition. Thus, at least under certain circumstances, medial rostral PFC appears to support attention toward the external environment, facilitating performance in situations that do not require extensive processing of experimental stimuli.

Adult↗
PubMed2006

Functional specialization within rostral prefrontal cortex (area 10): a meta-analysis.

One of the least well understood regions of the human brain is rostral prefrontal cortex, approximating Brodmann's area 10. Here, we investigate the possibility that there are functional subdivisions within this region by conducting a meta-analysis of 104 functional neuroimaging studies (using positron emission tomography/functional magnetic resonance imaging). Studies involving working memory and episodic memory retrieval were disproportionately associated with lateral activations, whereas studies involving mentalizing (i.e., attending to one's own emotions and mental states or those of other agents) were disproportionately associated with medial activations. Functional variation was also observed along a rostral-caudal axis, with studies involving mentalizing yielding relatively caudal activations and studies involving multiple-task coordination yielding relatively rostral activations. A classification algorithm was trained to predict the task, given the coordinates of each activation peak. Performance was well above chance levels (74% for the three most common tasks; 45% across all eight tasks investigated) and generalized to data not included in the training set. These results point to considerable functional segregation within rostral prefrontal cortex.

Algorithms↗
PubMed2005

Impairment of specific episodic memory processes by sub-psychotic doses of ketamine: the effects of levels of processing at encoding and of the subsequent retrieval task.

RATIONALE: The precise nature of the impact of the N-methyl-D-aspartate antagonist, ketamine, upon human episodic memory, has yet to be elucidated fully. OBJECTIVES: This study sought to assess the effects of ketamine on the sub-processes facilitating memory encoding and retrieval. METHODS: We evaluated the effects of the drug on a series of memory performance measures depending upon whether it was administered at the encoding or retrieval stage and on the nature of the encoding task used. Twelve healthy volunteers participated in a double-blind, placebo-controlled, randomized, within-subjects study. Intravenous infusions of placebo, 50 ng/ml ketamine or 100 ng/ml ketamine were administered. We investigated the effects of ketamine on three key aspects of episodic memory: encoding vs retrieval processes, source memory, and depth of processing. Data were analysed using both multinomial modelling and standard measures of item discrimination and response bias. RESULTS: Deleterious effects of ketamine on episodic memory were primarily attributable to its effects on encoding, rather than retrieval processes. Recognition memory was impaired for items encoded at an intermediate level of processing, but preserved for shallowly and deeply encoded items. Increased source guessing bias was also observed when encoding took place under ketamine. CONCLUSIONS: The effects of ketamine upon episodic memory seem, therefore, to predominate at encoding. Furthermore, our results are also consistent with a specific impairment of encoding processes that result in subsequent recollective, as opposed to familiarity-based, retrieval. The observed effects are compatible with memory deficits seen in schizophrenia and thus provide some support for the ketamine model of the disease.

Adolescent↗
PubMed2005

Distinct roles for lateral and medial anterior prefrontal cortex in contextual recollection.

A key feature of human recollection is the ability to remember details of the context in which events were experienced, as well as details of the events themselves. Previous studies have implicated a number of regions of prefrontal cortex in contextual recollection, but the role of anterior prefrontal cortex has so far resisted detailed characterization. We used event-related functional MRI (fMRI) to contrast recollection of two forms of contextual information: 1) decisions one had previously made about stimuli (task memory) and 2) which of two temporally distinct lists those stimuli had been presented in (list memory). In addition, a retrieval cue manipulation permitted evaluation of the stage of the retrieval process in which the activated regions might be involved. The results indicated that anterior prefrontal cortex responded significantly more during recollection of task than list context details. Furthermore, activation profiles for lateral and medial aspects of anterior prefrontal cortex suggested differing roles in recollection. Lateral regions seem to be more involved in the early retrieval specification stages of recollection, with medial regions contributing to later stages (e.g., monitoring and verification).

Adolescent↗
PubMed2005

Anterior prefrontal cortex and the recollection of contextual information.

Recollective memory can involve the retrieval of many different kinds of contextual information, including where and when an event took place, as well as our thoughts and feelings at the time. The brain regions associated with this ability were examined in an event-related fMRI experiment, where participants made decisions about words or famous faces which were presented either on the left or right of a monitor screen. Subsequently, the studied words and faces were again presented and participants underwent fMRI brain scanning while recollecting either which of the decisions they had made on each item ("task memory"), or whether it had been presented on the left or right of the screen ("position memory"). A functional dissociation was observed within anterior prefrontal cortex (principally Brodmann's area 10), with activation in lateral regions associated with remembering either type of information (relative to baseline), and a medial anterior PFC region showing significantly greater activation during the "task memory" conditions. These results suggest different roles for lateral and medial anterior prefrontal cortex in recollection.

Adult↗
PubMed2005

Failing to get the gist: reduced false recognition of semantic associates in semantic dementia.

In 2 experiments involving patients with semantic dementia, the authors investigated the impact of semantic memory loss on both true and false recognition. Experiment 1 involved recognition memory for categories of everyday objects that shared a predominantly semantic relationship. The patients showed preserved item-specific recollection for the pictorial stimuli but, compared with control participants, exhibited significantly reduced utilization of gist information regarding the categories of objects. The latter result is consistent with the patients' degraded semantic knowledge. Experiment 2 involved categories of abstract objects that were related to one another perceptually rather than semantically. Patients with semantic dementia obtained item-specific recollection and gist memory scores that were indistinguishable from those of control participants. These results suggest that the reduction in gist memory in semantic dementia is largely specific to semantic representations and cannot be attributed to general difficulty with abstracting and/or utilizing gistlike commonalities between stimuli.

Aged↗
PubMed2004

Graded recall success: an event-related fMRI comparison of tip of the tongue and feeling of knowing.

Insights into memory retrieval processes can be obtained by examining graded recall success, specifically, tip-of-the-tongue (TOT) and feeling-of-knowing (FOK) states. TOT is defined as a recall failure accompanied by a strong feeling of imminent retrieval, and FOK as a recall failure accompanied by a feeling of future ability to recognize the item. The present fMRI study examined the brain regions associated with both intermediate retrieval states in a within-subject, within-memory system design. Subjects were presented with general knowledge questions and were instructed to respond to each with one of four options: Know, indicating successful retrieval of the answer; TOT; FOK; or Don't know, indicating retrieval failure. Different patterns of activation in several brain regions including prefrontal cortex were associated with TOT and FOK states. For example, TOT was associated with activation in anterior cingulate, right dorsal and inferior, and bilateral anterior, prefrontal cortex. TOT and FOK elicited similar levels of activation in parietal regions, both significantly greater than that associated with Know and Don't know responses. The results are interpreted in the light of theories of the role of prefrontal cortex in recall and cognitive conflict.

Adolescent↗
PubMed2004

Specific- and partial-source memory: effects of aging.

Normal aging can be associated with impairments in source memory (recollecting an event's context). This study examined the effects of aging on specific-source memory (e.g., remembering which of 4 people spoke a word) and partial-source memory (e.g., remembering the gender of the person who spoke the word). When young and older adults were matched in terms of old-new recognition, age-related deficits were observed on both specific- and partial-source recollection. When the groups were matched on partial-source performance, no disproportionate specific-source impairment was seen. The results suggest that aging does not differentially affect specific- versus partial-source memory.

Adolescent↗
PubMed2004

Memory and emotions for the september 11, 2001, terrorist attacks in patients with Alzheimer's disease, patients with mild cognitive impairment, and healthy older adults.

National traumatic events can produce extremely vivid memories. Using a questionnaire administered during telephone interviews, the authors investigated emotional responses to, and memory for. the September 11, 2001, terrorist attacks in patients with Alzheimer's disease (AD), patients with mild cognitive impairment (MCI), and healthy older adults in the initial weeks following the event and again 3-4 months later. There were several notable findings. First, patients with AD showed less memory than patients with MCI and older adults. Second, patients with AD, but not patients with MCI or older adults, appeared to retain more memory for personal versus factual information. Third, patients with AD and older adults did not differ in the intensity of their reported emotional responses to the attacks, whereas patients with MCI reported relatively less intense emotional responses. Last, distortions of memory for personal information were frequent for all participants but were more common in patients with AD.

Aged↗
PubMed2003

Feeling-of-knowing in episodic memory: an event-related fMRI study.

An individual may fail to recall an item from memory but still feel that it would be recognized on a later test, a retrieval state termed the "feeling-of-knowing" (FOK). In this study we used event-related fMRI and the FOK to examine both encoding- and retrieval-related factors that are associated with different levels of recall performance: successful retrieval of a previously studied item, retrieval failure accompanied by the FOK, and retrieval failure without any FOK. The results revealed one predominant pattern of retrieval-related activation: an intermediate level of activation for FOK-less than that associated with successful recall and greater than that associated with unsuccessful recall (frontal and left parietal cortices). Two further patterns were also observed: greater activation for both successful recall and FOK than for unsuccessful recall (left midlateral prefrontal cortex) and greater activation for successful recall than for both FOK and unsuccessful recall (left MTL). Analysis of encoding trials conditional upon subsequent retrieval success revealed a pattern of activation that appeared to predict subsequent recall, but which further analysis indicated to be a better predictor of subsequent recognition. These results provide evidence that the phenomenology of graded recall is represented neurally in frontal and parietal cortices, but that activation at encoding may not precipitate the different levels of recall experience.

Adolescent↗
PubMed2003

Neural mechanisms of visual object priming: evidence for perceptual and semantic distinctions in fusiform cortex.

Previous functional imaging studies have shown that facilitated processing of a visual object on repeated, relative to initial, presentation (i.e., repetition priming) is associated with reductions in neural activity in multiple regions, including fusiform/lateral occipital cortex. Moreover, activity reductions have been found, at diminished levels, when a different exemplar of an object is presented on repetition. In one previous study, the magnitude of diminished priming across exemplars was greater in the right relative to the left fusiform, suggesting greater exemplar specificity in the right. Another previous study, however, observed fusiform lateralization modulated by object viewpoint, but not object exemplar. The present fMRI study sought to determine whether the result of differential fusiform responses for perceptually different exemplars could be replicated. Furthermore, the role of the left fusiform cortex in object recognition was investigated via the inclusion of a lexical/semantic manipulation. Right fusiform cortex showed a significantly greater effect of exemplar change than left fusiform, replicating the previous result of exemplar-specific fusiform lateralization. Right fusiform and lateral occipital cortex were not differentially engaged by the lexical/semantic manipulation, suggesting that their role in visual object recognition is predominantly in the visual discrimination of specific objects. Activation in left fusiform cortex, but not left lateral occipital cortex, was modulated by both exemplar change and lexical/semantic manipulation, with further analysis suggesting a posterior-to-anterior progression between regions involved in processing visuoperceptual and lexical/semantic information about objects. The results are consistent with the view that the right fusiform plays a greater role in processing specific visual form information about objects, whereas the left fusiform is also involved in lexical/semantic processing.

Adolescent↗
PubMed2002

Regional brain activations differ for semantic features but not categories.

Is human semantic knowledge neurally organised according to either category (e.g. living non-living) or attribute type (e.g. perceptual non-perceptual information)? Normal subjects were scanned using PET during a novel semantic production task, in which they generated either perceptual or non-perceptual information in response to names of living or non-living concepts. Analyses of blood flow in the temporal lobes revealed no significant differences associated with responses to living non-living concepts. Comparisons between retrieval of perceptual non-perceptual information, however, revealed significantly greater blood flow in left posterior inferior temporal cortex and right fusiform cortex associated with perceptual information and in left middle temporal cortex with non-perceptual information. These findings support a primarily attribute-based neural organisation of semantic knowledge.

Adult↗
PubMed2002

Recollection-based memory in frontotemporal dementia: implications for theories of long-term memory.

It has been convincingly demonstrated that patients with semantic dementia (the temporal variant of frontotemporal dementia) can show intact recognition memory for pictorial stimuli. As yet, the contribution made by recollective processes to this ability and the status of associated neural regions have not been investigated in the disease. Here, we used both a source monitoring paradigm and an associative memory test to evaluate the ability of patients with semantic dementia to use recollection-based memory processes, and a volumetric MRI technique to assess the extent of atrophy in the hippocampus. Although some patients showed impaired source and associative memory, many performed as well as control participants. Importantly, status of semantic knowledge, as measured by tests of comprehension and production, did not predict recollection-based memory ability. There was no significant positive correlation between recollection and volume of the hippocampus; instead, both source discrimination and associative memory correlated highly with performance on a battery of frontal lobe tests. Consistent with the view that damage to the prefrontal cortex might influence recollection performance, patients with the frontal variant of frontotemporal dementia, with atrophy largely confined to the frontal lobes, all performed at floor level on source discrimination. These results provide further compelling evidence in favour of the multiple input model of long-term memory and highlight the role of frontal lobe systems in recollection-based memory.

Aged↗
PubMedDate not supplied

fMRI evidence for separable and lateralized prefrontal memory monitoring processes.

Source memory research suggests that attempting to remember specific contextual aspects surrounding prior stimulus encounters results in greater left prefrontal cortex (PFC) activity than simple item-based old/new recognition judgments. Here, we tested a complementary hypothesis that predicts increases in the right PFC with tasks requiring close monitoring of item familiarity. More specifically, we compared a judgment of frequency (JOF) task to an item memory task, in which the former required estimating the number of previous picture encounters and the latter required discriminating old from new exemplars of previously seen items. In comparison to standard old/new recognition, both source memory and the JOF task examined here require more precise mnemonic judgments. However, in contrast to source memory, cognitive models suggest the JOF task relies heavily upon item familiarity, not specific contextual recollections. Event-related fMRI demonstrated greater recruitment of right, not left, dorsolateral and frontopolar PFC regions during the JOF compared to item memory task. These data suggest a role for right PFC in the close monitoring of the familiarity of objects, which becomes critical when contextual recollection is ineffective in satisfying a memory demand.

Adolescent↗