Toshikatsu Fujii

Memory repression: Brain mechanisms underlying dissociative amnesia

Dissociative amnesia usually follows a stressful event and cannot be attributable to explicit brain damage. It is thought to reflect a reversible deficit in memory retrieval probably due to memory repression. However, the neural mechanisms underlying this condition are not clear. We used fMRI to investigate neural activity associated with memory retrieval in two patients with dissociative amnesia. For each patient, three categories of face photographs and three categories of peoples names corresponding to the photographs were prepared: those of “recognizable” high school friends who were acquainted with and recognizable to the patients, those of “unrecognizable” colleagues who were actually acquainted with but unrecognizable to the patients due to their memory impairments, and “control” distracters who were unacquainted with the patients. During fMRI, the patients were visually presented with these stimuli and asked to indicate whether they were personally acquainted with them. In the comparison of the unrecognizable condition with the recognizable condition, we found increased activity in the pFC and decreased activity in the hippocampus in both patients. After treatment for retrograde amnesia, the altered pattern of brain activation disappeared in one patient whose retrograde memories were recovered, whereas it remained unchanged in the other patient whose retrograde memories were not recovered. Our findings provide direct evidence that memory repression in dissociative amnesia is associated with an altered pattern of neural activity, and they suggest the possibility that the pFC has an important role in inhibiting the activity of the hippocampus in memory repression.

Systematic retinotopic reaching error vectors in unilateral optic ataxia

The main aim of this study is to determine the reference frame of the pointing errors that characterize patients with unilateral optic ataxia (OA). The reaching errors of seven patients with unilateral OA when pointing on a 2D matrix in peripheral vision were investigated in order to better qualify the reference frame of their deficit. Patients were asked to fixate a central target and then to point at one of 24 visual targets presented in their left or right peripheral visual fields, with their left or right hands. The four left and the three right hemisphere lesion patients with OA exhibited an identical pattern of results. In the contralesional visual field, error vectors were systematically directed toward the fixation point, rather than horizontally toward the side of the lesion. OA results from a deficit in transforming targets eye-centred coordinates into appropriate motor commands.

The role of the dorsolateral prefrontal cortex in deception when remembering neutral and emotional events

We used functional magnetic resonance imaging (fMRI) to investigate the neural correlates of deception while remembering neutral events and emotional events. Before fMRI, subjects were presented with a series of neutral and emotional pictures and were asked to rate each picture for arousal. During fMRI, subjects were presented with the studied and nonstudied pictures and were asked to make an honest recognition judgment in response to half of the pictures and a dishonest response to the remaining half. We found that deception pertaining to the memory of neutral pictures was associated with increased activity in the bilateral dorsolateral prefrontal cortex, the left ventrolateral prefrontal cortex, and the left orbitofrontal cortex. We also found that deception while remembering emotional pictures was associated with increased activity in the bilateral dorsolateral prefrontal cortex. An overlapping activation between the two types of deception was found in the bilateral dorsolateral prefrontal cortex. Our results indicate that the dorsolateral prefrontal cortex is associated with the executive aspects of deception, regardless of the emotional valence of memory content.

Do parkinsonian patients have trouble telling lies? The neurobiological basis of deceptive behaviour

Parkinsons disease is a common neurodegenerative disorder with both motor symptoms and cognitive deficits such as executive dysfunction. Over the past 100 years, a growing body of literature has suggested that patients with Parkinsons disease have characteristic personality traits such as industriousness, seriousness and inflexibility. They have also been described as ‘honest’, indicating that they have a tendency not to deceive others. However, these personality traits may actually be associated with dysfunction of specific brain regions affected by the disease. In the present study, we show that patients with Parkinsons disease are indeed ‘honest’, and that this personality trait might be derived from dysfunction of the prefrontal cortex. Using a novel cognitive task, we confirmed that patients with Parkinsons disease (nu2009=u200932) had difficulty making deceptive responses relative to healthy controls (nu2009=u200920). Also, using resting-state 18F-fluorodeoxyglucose PET, we showed that this difficulty was significantly correlated with prefrontal hypometabolism. Our results are the first to demonstrate that the ostensible honesty found in patients with Parkinsons disease has a neurobiological basis, and they provide direct neuropsychological evidence of the brain mechanisms crucial for human deceptive behaviour.

Effects of emotion and reward motivation on neural correlates of episodic memory encoding: A PET study

It is known that emotion and reward motivation promote long-term memory formation. It remains unclear, however, how and where emotion and reward are integrated during episodic memory encoding. In the present study, subjects were engaged in intentional encoding of photographs under four different conditions that were made by combining two factors (emotional valence, negative or neutral; and monetary reward value, high or low for subsequent successful recognition) during H2 15O positron emission tomography (PET) scanning. As for recognition performance, we found significant main effects of emotional valence (negative>neutral) and reward value (high value>low value), without an interaction between the two factors. Imaging data showed that the left amygdala was activated during the encoding conditions of negative pictures relative to neutral pictures, and the left orbitofrontal cortex was activated during the encoding conditions of high reward pictures relative to low reward pictures. In addition, conjunction analysis of these two main effects detected right hippocampal activation. Although we could not find correlations between recognition performance and activity of these three regions, we speculate that the right hippocampus may integrate the effects of emotion (processed in the amygdala) and monetary reward (processed in the orbitofrontal cortex) on episodic memory encoding.

The contribution of the dorsolateral prefrontal cortex to the preparation for deception and truth-telling.

Recent neuroimaging evidence suggests that the dorsolateral prefrontal cortex is associated with creating deceptive responses. However, the neural basis of the preparatory processes that create deception has yet to be explored. Previous neuroimaging studies have demonstrated that the preparation for a certain task activates brain areas relevant to the execution of that task, leading to the question of whether dorsolateral prefrontal activity is observed during the preparation for deception. In the present study, we used functional magnetic resonance imaging (fMRI) to determine whether dorsolateral prefrontal activity, which increases during the execution of deception compared with the execution of truth-telling, also increases during the preparation for deception compared with the preparation for truth-telling. Our data show that the execution of deception was associated with increased activity in several brain regions, including the left dorsolateral prefrontal cortex, compared with truth-telling, confirming the contribution of this region to the production of deceptive responses. The results also reveal that the preparations for both deception and truth-telling were associated with increased activity in certain brain regions, including the left dorsolateral prefrontal cortex. These findings suggest that the preparations for truth-telling and deception make similar demands on the brain and that the dorsolateral prefrontal activity identified in the preparation phase is associated with general preparatory processes, regardless of whether one is telling a lie or the truth.

False item recognition in patients with Alzheimer's disease

Recent evidence suggests that patients with Alzheimers disease (AD), as compared with normal individuals, exhibit increased false recognition by stimulus repetition in the Deese-Roediger-McDermott (DRM) task or associative recognition memory tasks, probably due to impaired recollection-based monitoring. However, because of possible alternative explanations for the findings of these previous studies, the evidence for impaired recollection-based monitoring in AD patients remains inconclusive. In this study, we employed stimulus repetition in old/new recognition judgments of single-item picture memory without a factor of association between the stimuli and examined whether AD patients showed increased false item recognition as compared with healthy controls. AD patients and healthy controls studied single-item pictures presented either once or three times. They were later asked to make an old/new recognition judgment in response to (a) Same pictures, pictures identical to those seen at encoding, (b) Similar lures, novel pictures similar to but not identical to those seen at encoding, and (c) Dissimilar lures, novel pictures not similar to those seen at encoding. For Same pictures, repeated presentation of stimuli increased the proportion of old responses in both groups. For Similar lures, repeated presentation of stimuli increased the rate of old responses in AD patients but not in control subjects. The results of the present study clearly demonstrated elevated false recognition by stimulus repetition in single-item recognition in AD patients. The present findings strongly support the view that AD patients are impaired in their ability to use item-specific recollection in order to avoid false recognition.

Small gray matter volume in orbitofrontal cortex in Prader-Willi syndrome: a voxel-based MRI study.

Prader‐Willi syndrome (PWS) is a genetically determined neurodevelopmental disorder presenting with behavioral symptoms including hyperphagia, disinhibition, and compulsive behavior. The behavioral problems in individuals with PWS are strikingly similar to those in patients with frontal pathologies, particularly those affecting the orbitofrontal cortex (OFC). However, neuroanatomical abnormalities in the frontal lobe have not been established in PWS. The aim of this study was to look, using volumetric analysis, for morphological changes in the frontal lobe, especially the OFC, of the brains of individuals with PWS. Twelve adults with PWS and 13 age‐ and gender‐matched control subjects participated in structural magnetic resonance imaging (MRI) scans. The whole‐brain images were segmented and normalized to a standard stereotactic space. Regional gray matter volumes were compared between the PWS group and the control group using voxel‐based morphometry. The PWS subjects showed small gray‐matter volume in several regions, including the OFC, caudate nucleus, inferior temporal gyrus, precentral gyrus, supplementary motor area, postcentral gyrus, and cerebellum. The small gray‐matter volume in the OFC remained significant in a separate analysis that included total gray matter volume as a covariate. These preliminary findings suggest that the neurobehavioral symptoms in individuals with PWS are related to structural brain abnormalities in these areas. Hum Brain Mapp, 2011.

MR Imaging of Subcallosal Artery Infarct Causing Amnesia after Surgery for Anterior Communicating Artery Aneurysm

BACKGROUND AND PURPOSE: During surgery to treat an aneurysm in the anterior communicating artery, injury to the subcallosal artery, a perforator of the anterior communicating artery, may lead to infarction that produces basal forebrain amnesia after surgery. Our purpose was to examine whether 3D MR imaging can detect subcallosal artery infarction in patients with amnesia after surgery for an anterior communicating artery aneurysm. MATERIALS AND METHODS: We evaluated 3D–T2-weighted MR images obtained a median of 4 months after treatment of anterior communicating artery aneurysm for the presence of infarcted foci in 10 consecutive patients with postoperative amnesia. Because the subcallosal artery and its neighboring perforator, the recurrent artery of Heubner, were considered the most easily affected vessels during that surgery, we focused mainly on 8 regions of the subcallosal artery territory per hemisphere and 5 regions of the recurrent artery of Heubner territory per hemisphere. RESULTS: All 10 patients had infarcts in the territory of the subcallosal artery (median, 9 regions per patient), and most were bilateral (9 of 10 patients). Five patients had additional infarcted foci in the territory of the recurrent artery of Heubner (median, 1 region per patient), all unilateral. Among the regions perfused by the subcallosal artery, the column of the fornix was involved in all patients; the anterior commissure, in 9; and the paraterminal gyrus, in 8 patients. CONCLUSIONS: 3D MR imaging revealed subcallosal artery infarction, the distribution of which was mostly bilateral, presumably owing to the unpairedness of that artery, in patients with postoperative amnesia after anterior communicating artery aneurysm repair.

Neural correlates of forgiveness for moral transgressions involving deception

We used positron emission tomography (PET) to investigate the neural mechanisms underlying the willingness to forgive another persons moral transgression involving deception. During scanning, 12 subjects were asked to judge the forgivability of a perpetrators moral transgression. These transgressions were described by four kinds of scenarios composed of a combination of two factors: the attitude of the perpetrator (dishonest or honest) and the severity of the moral transgression (serious or minor). Behavioral data showed that both the perpetrators dishonesty and the seriousness of the scenario decreased the subjects willingness to forgive the moral transgression. Neuroimaging data revealed that, relative to honest responses, a perpetrators dishonest responses were associated with right ventromedial prefrontal activity, which possibly reflects the subjects identification of the perpetrators deception. The opposite comparison did not show significant activation. Moreover, a comparison of serious scenarios with minor scenarios did not reveal significant activation. Instead, minor scenarios, relative to serious scenarios, evoked activity in the right middle frontal gyrus and the right caudate nucleus, possibly reflecting increased demand on frontal control system function. Further analysis revealed that the left ventromedial prefrontal cortex showed a significant interaction between the two factors, indicating that this region functions as a mediator of the two factors, modulating judgments regarding the forgivability of moral transgressions. Taken together, these findings suggest that the ventromedial prefrontal cortex plays a key role in the forgiveness of moral transgressions involving deception.