Altered basal forebrain BOLD signal variability at rest in posttraumatic stress disorder: A potential candidate vulnerability mechanism for neurodegeneration in PTSD.

Individuals with posttraumatic stress disorder (PTSD) are at increased risk for the development of various forms of dementia. Nevertheless, the neuropathological link between PTSD and neurodegeneration remains unclear. Degeneration of the human basal forebrain constitutes a pathological hallmark of neurodegenerative diseases, such as Alzheimer's and Parkinson's disease. In this seed-based resting-state (rs-)fMRI study identifying as outcome measure the temporal BOLD signal fluctuation magnitude, a seed-to-voxel analyses assessed temporal correlations between the average BOLD signal within a bilateral whole basal forebrain region-of-interest and each whole-brain voxel among individuals with PTSD (n = 65), its dissociative subtype (PTSD+DS) (n = 38) and healthy controls (n = 46). We found that compared both with the PTSD and healthy controls groups, the PTSD+DS group exhibited increased BOLD signal variability within two nuclei of the seed region, specifically in its extended amygdaloid region: the nucleus accumbens and the sublenticular extended amygdala. This finding is provocative, because it mimics staging models of neurodegenerative diseases reporting allocation of neuropathology in early disease stages circumscribed to the basal forebrain. Here, underlying candidate etiopathogenetic mechanisms are neurovascular uncoupling, decreased connectivity in local- and large-scale neural networks, or disrupted mesolimbic dopaminergic circuitry, acting indirectly upon the basal forebrain cholinergic pathways. These abnormalities may underpin reward-related deficits representing a putative link between persistent traumatic memory in PTSD and anterograde memory deficits in neurodegeneration. Observed alterations of the basal forebrain in the dissociative subtype of PTSD point towards the urgent need for further exploration of this region as a potential candidate vulnerability mechanism for neurodegeneration in PTSD.

Large-Scale Functional Brain Network Architecture Changes Associated With Trauma-Related Dissociation.

OBJECTIVE: Dissociative experiences commonly occur in response to trauma, and while their presence strongly affects treatment approaches in posttraumatic spectrum disorders, their etiology remains poorly understood and their phenomenology incompletely characterized. Methods to reliably assess the severity of dissociation symptoms, without relying solely on self-report, would have tremendous clinical utility. Brain-based measures have the potential to augment symptom reports, although it remains unclear whether brain-based measures of dissociation are sufficiently sensitive and robust to enable individual-level estimation of dissociation severity based on brain function. The authors sought to test the robustness and sensitivity of a brain-based measure of dissociation severity. METHODS: An intrinsic network connectivity analysis was applied to functional MRI scans obtained from 65 women with histories of childhood abuse and current posttraumatic stress disorder (PTSD). The authors tested for continuous measures of trauma-related dissociation using the Multidimensional Inventory of Dissociation. Connectivity estimates were derived with a novel machine learning technique using individually defined homologous functional regions for each participant. RESULTS: The models achieved moderate ability to estimate dissociation, after controlling for childhood trauma and PTSD severity. Connections that contributed the most to the estimation mainly involved the default mode and frontoparietal control networks. By contrast, all models performed at chance levels when using a conventional group-based network parcellation. CONCLUSIONS: Trauma-related dissociative symptoms, distinct from PTSD and childhood trauma, can be estimated on the basis of network connectivity. Furthermore, between-network brain connectivity may provide an unbiased estimate of symptom severity, paving the way for more objective, clinically useful biomarkers of dissociation and advancing our understanding of its neural mechanisms.

Individual differences in corticolimbic structural profiles linked to insecure attachment and coping styles in motor functional neurological disorders.

BACKGROUND: Insecure attachment and maladaptive coping are important predisposing vulnerabilities for Functional Neurological Disorders (FND)/Conversion Disorder, yet no prior structural neuroimaging studies have investigated biomarkers associated with these risk factors in FND populations. This magnetic resonance imaging study examined cortical thickness and subcortical volumes associated with self-reported attachment and coping styles in patients with FND. We hypothesized that insecure attachment and maladaptive coping would relate to limbic-paralimbic structural alterations. METHODS: FreeSurfer cortical thickness and subcortical volumetric analyses were performed in 26 patients with motor FND (21 women; 5 men) and 27 healthy controls (22 women; 5 men). For between-group comparisons, patients with FND were stratified by Relationship Scales Questionnaire, Ways of Coping Scale-Revised, and Connor-Davidson Resilience Scale scores. Within-group analyses were also performed in patients with FND. All analyses were performed in the complete cohort and separately in women only to evaluate for gender-specific effects. Cortical thickness analyses were whole-brain corrected at the cluster-wise level; subcortical analyses were Bonferroni corrected. RESULTS: In women with FND, dismissing attachment correlated with reduced left parahippocampal cortical thickness. Confrontive coping was associated with reduced right hippocampal volume, while accepting responsibility positively correlated with right precentral gyrus cortical thickness. These findings held adjusting for anti-depressant use. All FND-related findings were within the normal range when compared to healthy women. CONCLUSION: These observations connect individual-differences in limbic-paralimbic and premotor structures to attachment and coping styles in FND. The relationship between parahippocampal thickness and dismissing attachment may indicate aberrant social-emotional and contextual appraisal in women with FND.

The trauma factor: Examining the relationships among different types of trauma, dissociation, and psychopathology.

Extensive research has reported a dose-response relationship between exposure to trauma and the severity of both dissociation and psychopathology. However, certain types of trauma may co-occur more frequently than others and specific combinations of traumatic experiences may relate differently to dissociative processes and psychiatric symptoms. In the current study, 359 adult participants completed questionnaires on traumatic experiences, dissociation, and psychopathology. A correlation network analysis showed that some types of trauma are more likely to co-occur and that especially traumatic experiences in attachment relationships during childhood were significantly associated with other trauma in life. A latent class analysis identified four classes of participants (namely, extremely traumatized, resilient to the impact of abuse, exposed to impersonal and social trauma, and reporting low levels of traumatization) who showed different profiles on trauma exposure, dissociation, and psychopathology. Mediation analyses further showed that dissociation partially mediated the relationship between different types of traumatic experiences and the severity of psychiatric symptoms. The findings of this study support the view that a comprehensive assessment of traumatic experiences and dissociation is needed in trauma research and clinical practice.

Dissociative experiences and dissociative minds: Exploring a nomological network of dissociative functioning.

In this study, the psychometric properties of the Dissociative Experiences Scale-II (DES-II) were tested in a sample of Italian adults, and a nomological network of dissociative functioning based on current psychodynamic research was examined. A total of 794 participants (55% females) ranging in age from 18 to 64 completed the DES-II and other measures of theory of mind, alexithymia, attachment style, and empathy. The Italian translation of the DES-II showed high internal consistency, adequate item-to-scale homogeneity, and good split-half reliability. A single-factor solution including the 8 items of pathological dissociation (DES-T) adequately fit the data. Participants who reported higher levels of dissociative experiences showed significantly lower scores on theory of mind and empathy than other participants. They also showed significantly higher scores on alexithymia, preoccupied attachment, and fearful attachment. Results of the study support the view that people who suffer from severe dissociative experiences may also have difficulties mentalizing and regulating affects and that they may feel uncomfortable in close relationships because they have a negative view of the self. This can inform clinical work with dissociative individuals, who could benefit from therapies that consider their potential problems with mentalization, empathy, affect regulation, and attachment.

Tracking down the footprints of bad paternal relationships in dissociative disorders: A diffusion tensor imaging study.

Preclinical studies indicate that stress early in life can cause long-term alterations in brain development. Studies have shown alterations in the brain functions of patients after experiencing trauma. Our aim is to examine whether the integrity of white matter tracts might be affected in dissociative disorder (DD) patients. A total of 15 DD patients and 15 healthy controls were studied, with the groups matched by age and gender. Diffusion-weighted echoplanar brain images were obtained using a 1.5 Tesla magnetic resonance imaging scanner. Regions of interest were manually placed on directional maps based on principal anisotropy. Apparent diffusion coefficient and fractional anisotropy (FA) values of white matter were measured bilaterally in the anterior corona radiata (ACR) and by diffusion tensor imaging in the genu and splenium of the corpus callosum. Significantly lower FA values were observed in the right ACR of DD patients versus healthy individuals. We also found an association between bad paternal relationships and lower FA in the genu of the corpus callosum in female patients. Alterations in the right ACR suggest that diffusion anisotropy measurement can be used as a quantitative biomarker for DD. Paternal relationships may also affect the brain's microstructure in women with DD.

Common and Dissociable Dysfunction of the Reward System in Bipolar and Unipolar Depression.

Unipolar and bipolar depressive episodes have a similar clinical presentation that suggests common dysfunction of the brain's reward system. Here, we evaluated the relationship of both dimensional depression severity and diagnostic category to reward system function in both bipolar and unipolar depression. In total, 89 adults were included, including 27 with bipolar depression, 25 with unipolar depression, and 37 healthy comparison subjects. Subjects completed both a monetary reward task and a resting-state acquisition during 3T BOLD fMRI. Across disorders, depression severity was significantly associated with reduced activation for wins compared with losses in bilateral ventral striatum, anterior cingulate cortex, posterior cingulate cortex, and right anterior insula. Resting-state connectivity within this reward network was also diminished in proportion to depression severity, most notably connectivity strength in the left ventral striatum. In addition, there were categorical differences between patient groups: resting-state connectivity at multiple reward network nodes was higher in bipolar than in unipolar depression. Reduced reward system task activation and resting-state connectivity therefore appear to be a brain phenotype that is dimensionally related to depression severity in both bipolar and unipolar depression. In contrast, categorical differences in reward system resting connectivity between unipolar and bipolar depression may reflect differential risk of mania. Reward system dysfunction thus represents a common brain mechanism with relevance that spans categories of psychiatric diagnosis.

The Dissociative Subtype of Posttraumatic Stress Disorder: Unique Resting-State Functional Connectivity of Basolateral and Centromedial Amygdala Complexes.

Previous studies point towards differential connectivity patterns among basolateral (BLA) and centromedial (CMA) amygdala regions in patients with posttraumatic stress disorder (PTSD) as compared with controls. Here we describe the first study to compare directly connectivity patterns of the BLA and CMA complexes between PTSD patients with and without the dissociative subtype (PTSD+DS and PTSD-DS, respectively). Amygdala connectivity to regulatory prefrontal regions and parietal regions involved in consciousness and proprioception were expected to differ between these two groups based on differential limbic regulation and behavioral symptoms. PTSD patients (n=49) with (n=13) and without (n=36) the dissociative subtype and age-matched healthy controls (n=40) underwent resting-state fMRI. Bilateral BLA and CMA connectivity patterns were compared using a seed-based approach via SPM Anatomy Toolbox. Among patients with PTSD, the PTSD+DS group exhibited greater amygdala functional connectivity to prefrontal regions involved in emotion regulation (bilateral BLA and left CMA to the middle frontal gyrus and bilateral CMA to the medial frontal gyrus) as compared with the PTSD-DS group. In addition, the PTSD+DS group showed greater amygdala connectivity to regions involved in consciousness, awareness, and proprioception-implicated in depersonalization and derealization (left BLA to superior parietal lobe and cerebellar culmen; left CMA to dorsal posterior cingulate and precuneus). Differences in amygdala complex connectivity to specific brain regions parallel the unique symptom profiles of the PTSD subgroups and point towards unique biological markers of the dissociative subtype of PTSD.

Dissociating the ability and propensity for empathy.

Neuroimaging suggests psychopaths have reduced vicarious activations when simply witnessing pain but less so when asked to empathize. This inspired us to distinguish the ability from the propensity to empathize. We argue that (i) this ability-propensity distinction is crucial to characterizing empathy in psychiatric disorders such as psychopathy and autism, (ii) that costly helping might be best predicted by the propensity for empathy, and (iii) suggest how social neuroscientists can start exploring this distinction.

Memories of attachment hamper EEG cortical connectivity in dissociative patients.

In this study, we evaluated cortical connectivity modifications by electroencephalography (EEG) lagged coherence analysis, in subjects with dissociative disorders and in controls, after retrieval of attachment memories. We asked thirteen patients with dissociative disorders and thirteen age- and sex-matched healthy controls to retrieve personal attachment-related autobiographical memories through adult attachment interviews (AAI). EEG was recorded in the closed eyes resting state before and after the AAI. EEG lagged coherence before and after AAI was compared in all subjects. In the control group, memories of attachment promoted a widespread increase in EEG connectivity, in particular in the high-frequency EEG bands. Compared to controls, dissociative patients did not show an increase in EEG connectivity after the AAI. Conclusions: These results shed light on the neurophysiology of the disintegrative effect of retrieval of traumatic attachment memories in dissociative patients.

Disociación psicomorga y somatomorfa en la infancia y adolescencia. a propósito de un caso / Somatoform dissociation in childhood and adolescence. A case report

A pesar de la mayor prevalencia en población infantil y adolescente de trastornos disociativos y conversivos, existen pocos casos en la literatura que realicen una descripción detallada de la biografía, la clínica y el encuadre psicoterapéutico con el que se ha trabajado. Se realiza una revisión de las características de estos trastornos en dicha población para posteriormente aportar un marco de intervención basado en las experiencias de trauma y apego, con especial hincapié en el procesamiento de las emociones (AU)

Despite the greater prevalence of dissociation and conversion disorders in childhood and adolescence, few reports including a detailed description of the case, the psychobiography and the psychotherapeutic formulation are available. The main features concerning these disorders for this population group are exposed. A trauma/attachment based psychotherapeutic intervention, with special emphasis in the emotion regulation role, is presented in this work (AU)

[Delusional disorder, autoaggression und suicide]. / Wahnerkrankung, Autoaggression und Suizid.

The authors report on the suicide of a 27-year-old woman with extreme self-inflicted injuries. The victim suffered from schizophrenic psychosis with several stays in mental institutions and one previous suicide attempt. Autopsy revealed multiple cut and stab injuries in various body regions (51 stabs to the chest, cutting off parts of ears and nose, stab to the eye and transection of the scalp). Death was caused by exsanguination.

Egocentric virtual maze learning in adult survivors of childhood abuse with dissociative disorders: evidence from functional magnetic resonance imaging.

Present neuroimaging findings suggest two subtypes of trauma response, one characterized predominantly by hyperarousal and intrusions, and the other primarily by dissociative symptoms. The neural underpinnings of these two subtypes need to be better defined. Fourteen women with childhood abuse and the current diagnosis of dissociative amnesia or dissociative identity disorder but without posttraumatic stress disorder (PTSD) and 14 matched healthy comparison subjects underwent functional magnetic resonance imaging (fMRI) while finding their way in a virtual maze. The virtual maze presented a first-person view (egocentric), lacked any topographical landmarks and could be learned only by using egocentric navigation strategies. Participants with dissociative disorders (DD) were not impaired in learning the virtual maze when compared with controls, and showed a similar, although weaker, pattern of activity changes during egocentric learning when compared with controls. Stronger dissociative disorder severity of participants with DD was related to better virtual maze performance, and to stronger activity increase within the cingulate gyrus and the precuneus. Our results add to the present knowledge of preserved attentional and visuospatial mnemonic functioning in individuals with DD.

Motivación psicológica en los juegos de rol online: un estudio de jugadores españoles del World of Warcraft / Psychological motivation in online role-playing games: A study of Spanish World of Warcraft players

La popularidad de los videojuegos ha aumentado considerablemente en los últimos años, convirtiéndose en uno de los mayores productos de ocio siendo los Juegos de Rol Online (MMORPGs) uno de los mayores exponentes; sin embargo, también ha aumentado la sospecha y alarma social de que puedan poseer cierto potencial adictivo enmarcado en el contexto de las adicciones conductuales o que los usuarios puedan desarrollar conductas desadaptativas entorno a esta tecnología. El objetivo del presente estudio evalúa las motivaciones psicológicas para jugar al al World of Warcraft (WoW) y las relaciona con variables sociodemográficas y estilos de juego. Se aplicó un cuestionario para evaluar diferentes motivaciones online a un colectivo de jugadores de WoW. A partir de una muestra final de 253 jugadores españoles (hombres jóvenes) el análisis factorial mostró la presencia de cuatro motivos de juego: socialización, exploración, logro y disociación. Además, los jugadores españoles, preferían el entorno Jugador contar Jugador, un aspecto que parece prevenir las potenciales consecuencias negativas al impedir el juego solitario. Los resultados indican que una de las motivaciones más importantes es la socialización y el estilo de Jugador contra Jugador, lo cual indica en gran parte el uso de este juego se hace de forma psicológicamente adaptativo (AU)

The popularity of playing videogames has increased considerably during the last few decades, and has become one of the most popular leisure activities worldwide. Some of the most popular game types are the Massively Multiplayer Online Role-Playing Games (MMORPGs). However, there has also been increased suspicion and social alarm that these games may possess an addictive potential, similar to other behavioural addictions, and that the user may develop maladaptive behaviours with respect to these games. The purpose of the present study was to assess the psychological motivations of playing World of Warcraft (WoW) and to relate them to sociodemographic variables and gaming styles. A questionnaire for assessing these motivations was developed and applied online to a collective of games. The final sample comprised 253 Spanish WoW players (all young males). Factor analysis of the questionnaire scores showed the presence of four motivations for gaming: socialisation, exploration, achievement, and dissociation. Results indicated that socialisation was one of the main motivational factors and that the gamers preferred the Player-versus-Player environment. Both of these aspects appear to be factors that may prevent potentially negative outcomes by inhibiting solitary play (AU)

Dissociable effects of subtotal lesions within the macaque orbital prefrontal cortex on reward-guided behavior.

The macaque orbital prefrontal cortex (PFo) has been implicated in a wide range of reward-guided behaviors essential for efficient foraging. The PFo, however, is not a homogeneous structure. Two major subregions, distinct by their cytoarchitecture and connections to other brain structures, compose the PFo. One subregion encompasses Walker's areas 11 and 13 and the other centers on Walker's area 14. Although it has been suggested that these subregions play dissociable roles in reward-guided behavior, direct neuropsychological evidence for this hypothesis is limited. To explore the independent contributions of PFo subregions to behavior, we studied rhesus monkeys (Macaca mulatta) with restricted excitotoxic lesions targeting either Walker's areas 11/13 or area 14. The performance of these two groups was compared to that of a group of unoperated controls on a series of reward-based tasks that has been shown to be sensitive to lesions of the PFo as a whole (Walker's areas 11, 13, and 14). Lesions of areas 11/13, but not area 14, disrupted the rapid updating of object value during selective satiation. In contrast, lesions targeting area 14, but not areas 11/13, impaired the ability of monkeys to learn to stop responding to a previously rewarded object. Somewhat surprisingly, neither lesion disrupted performance on a serial object reversal learning task, although aspiration lesions of the entire PFo produce severe deficits on this task. Our data indicate that anatomically defined subregions within macaque PFo make dissociable contributions to reward-guided behavior.

Double dissociation between syntactic gender and picture naming processing: a brain stimulation mapping study.

Neural foundations of syntactic gender processing remain poorly understood. We used electrostimulation mapping in nine right-handed awake patients during surgery for a glioma within the left hemisphere, to study whether the cortico-subcortical structures involved in naming versus syntactic gender processing are common or distinct. In French, the article determines the grammatical gender. Thus, the patient was asked to perform a picture naming task and to give the appropriate article for each picture, with and without stimulation. Cortical stimulation elicited reproducible syntactic gender disturbances in six patients, in the inferior frontal gyrus (three cases), and in the posterior middle temporal gyrus (three cases). Interestingly, no naming disorders were generated during stimulation of the syntactic sites, while cortical areas inducing naming disturbances never elicited grammatical gender errors when stimulated. Moreover, at the subcortical level, stimulation of the white matter lateral to the caudate nucleus induced gender errors in three patients, with no naming disorders. Using cortico-subcortical electrical mapping in awake patients, we demonstrate for the first time (1) a double dissociation between syntactic gender and naming processing, supporting independent network model rather than serial theory, (2) the involvement of the left inferior frontal gyrus, especially the pars triangularis, and the posterior left middle temporal gyrus in grammatical gender processing, (3) the existence of white matter pathways, likely a sub-part of the left superior longitudinal fasciculus, underlying a large-scale distributed cortico-subcortical circuit which might selectively sub-serve syntactic gender processing, even if interconnected with parallel sub-networks involved in naming (semantic and phonological) processing.

Dissociation in hysteria and hypnosis: evidence from cognitive neuroscience.

Jean-Martin Charcot proposed the radical hypothesis that similar brain processes were responsible for the unexplained neurological symptoms of 'hysteria', now typically diagnosed as 'conversion disorder' or 'dissociative (conversion) disorder', and the temporary effects of hypnosis. While this idea has been largely ignored, recent cognitive neuroscience studies indicate that (i) hypnotisability traits are associated with a tendency to develop dissociative symptoms in the sensorimotor domain; (ii) dissociative symptoms can be modelled with suggestions in highly hypnotisable subjects; and (iii) hypnotic phenomena engage brain processes similar to those seen in patients with symptoms of hysteria. One clear theme to emerge from the findings is that 'symptom' presentation, whether clinically diagnosed or simulated using hypnosis, is associated with increases in prefrontal cortex activity suggesting that intervention by the executive system in both automatic and voluntary cognitive processing is common to both hysteria and hypnosis. Nevertheless, while the recent literature provides some compelling leads into the understanding of these phenomena, the field still lacks well controlled systematically designed studies to give a clear insight into the neurocognitive processes underlying dissociation in both hysteria and hypnosis. The aim of this review is to provide an agenda for future research.

Trastorno disociativo y acontecimientos traumáticos. Un estudio en población española / Dissociative disorder and traumatic events. A study of Spanish population

El trastorno disociativo es una patología relativamente poco frecuente que se ha asociado a la presencia de acontecimientos traumáticos en la infancia y, especialmente, a los abusos sexuales. Nuestro estudio presenta una muestra clínica de 36 pacientes que padecen un trastorno disociativo, evaluados prospectivamente mediante escalas estandarizadas en las consultas habituales de psiquiatría general. La muestra se compone básicamente de mujeres (34/36), casadas (86,1%), de clase media-baja y con una importante comorbilidad (38,9 % trastornos afectivos, 52,8% de conversión, 41,7% de ansiedad y/o 38,9% trastornos de personalidad). Nuestros resultados muestran una alta tasa de acontecimientos traumáticos en la infancia (58,3 %) y de antecedentes de abusos sexuales (27,8%) en esta población, así como de otros acontecimientos traumáticos (55,6 %) en la edad adulta. La prevalencia de cualquier acontecimiento traumático (27/36) es más alta que en población general española, pero sólo discretamente para el caso de los abusos sexuales en la infancia. La gravedad de las puntuaciones de acontecimientos traumáticos correlaciona con la gravedad de la clínica disociativa. La presencia de acontecimientos traumáticos en la infancia de tipo sexual se asocian con la gravedad de la clínica disociativa medida con la Escala de disociación DES. En nuestra muestra, la edad del primer acontecimiento traumático no muestra relación con la gravedad de la clínica disociativa. Los antecedentes de abusos sexuales en la infancia (y no otros) también se relacionan con una mayor presencia de trastornos afectivos y conversivos (AU)

Dissociative Disorder is relatively uncommon. It has been associated to the presence of traumatic events and especially to sexual abuse in childhood. Our study presents a clinical sample of 36 patients with Dissociative Disorder, prospectively evaluated with standardized scales in an outpatient department of general psychiatry. The sample is mainly made up of married (86.1%) women (34/36), from medium-low class with important comorbidity (38.9% affective disorders, 52.8% conversive disorders, 41.7% anxiety disorders and 38.9%, personality disorders). Our results show a high rate of childhood traumatic events (58.3%) and a background of sexual abuse (27.8%) in this population as well as other traumatic events in adulthood (55.6%). The prevalence of any traumatic event (27/36) is higher than in general spanish population. However sexual abuse is only slightly higher than the estimated rate of sexual abuse in childhood. Higher scores in the traumatic event scale are correlated with the severity of dissociative symptoms. Only traumatic sexual traumas in childhood correlate with the severity of dissociative features measured by the DES (Dissociative Experiences Scale). Age of the first traumatic event does not correlates with the severity of dissociative symptoms. A background of traumatic sexual abuse in childhood is the only factor related with higher presence of comorbid affective disorders and conversive disorders (AU)

A double dissociation between somatosensory processing for perception and action.

Human neuropsychology suggests that there are two distinct body representations. Body image and body schema are, respectively, thought to be involved in conscious perceptual judgments and unconscious sensorimotor guidance. The evidence is based on the double dissociation between disorders of perceptual detection and sensorimotor guidance. Until now, research focused on cases that had impaired tactile pressure sensitivity and comparisons of performance were of cases suffering from different types of lesions (peripheral and central). Here, we report a unique double dissociation in two stroke patients with intact basic somatosensory processing (tactile detection). One patient was poor at identifying the position of where she had been touched on a line drawing of a hand, but was able to point accurately towards the actual position on her/his hand itself. The reverse pattern was observed in the other patient. This finding provides further support for separate processing for body image and body scheme.

Structural dissociation of attentional control and memory in adults with and without mild traumatic brain injury.

Memory and attentional control impairments are the two most common forms of dysfunction following mild traumatic brain injury (TBI) and lead to significant morbidity in patients, yet these functions are thought to be supported by different brain networks. This 3 T magnetic resonance diffusion tensor imaging (DTI) study investigates whether microstructural integrity of white matter, as measured by fractional anisotropy (FA) within a small set of individually localized regions of interest (ROIs), is associated with these cognitive domains in normal adults and adults with mild TBI. Results in a sample of 23 normal controls reveal a significant correlation between attentional control and FA within a ROI in the left hemisphere anterior corona radiata. Furthermore, the controls demonstrate a correlation between memory performance and FA in a ROI placed in the uncinate fasciculus. Next, to examine whether these relationships are found in the pathological ranges of attention, memory and microstructural white matter integrity associated with mild TBI, these analyses were applied to a group of 43 mild TBI patients. Results, which generally demonstrated a wider range of attention, memory and FA scores, replicated the correlation between attentional control and FA in left hemisphere anterior corona radiata, as well as the correlation between memory performance and FA in the uncinate fasciculus. These two sets of brain-behaviour relationships were highly specific, as shown by a lack of correlation between attention and uncinate fasciculus FA and the lack of correlation between memory performance and anterior corona radiata FA. Furthermore, a 'correlational double dissociation' was demonstrated to exist between two distinct frontal structures independently associated with attention and memory, respectively, via a series of multiple regression analyses in both normal controls and adults with mild TBI. The results of the multiple regression analyses provide direct evidence that tract-specific variation in microstructural white matter integrity among normal controls and among mild TBI patients can account for much of the variation in performance in specific cognitive domains. More generally, such findings suggest that diffusion anisotropy measurement can be used as a quantitative biomarker for neurocognitive function and dysfunction.