Biomedical subjects

Christine Mohr

Publications and source records attributed to Christine Mohr.

At least 19 recordsLinked to original sources

PubMed2007

Duration and not strength of activation in temporo-parietal cortex positively correlates with schizotypy.

Impaired self- and own body processing in patients with schizophrenia and individuals along the schizophrenia spectrum have been associated with dysfunctional cortical activation at the temporo-parietal junction. Here we investigated whether strength or duration of temporo-parietal junction activation during an own body processing task correlates with level of abnormal self-processing in healthy subjects as measured by the frequency of spontaneously experienced schizotypal body schema alterations (perceptual aberrations) and dissociative experiences. Participants carried out a mental imagery task with respect to their own body. Behavioral data and high density EEG were measured. EEG data were analyzed using evoked potential mapping and electrical neuroimaging. Participants completed two validated self-report questionnaires, one asking about perceptual aberration and one about dissociative experiences. The own body transformation task activated the right temporo-parietal junction at 310-390 ms. Participants' reaction times and duration of activation at the right temporo-parietal junction, but not its strength, were found to correlate positively with perceptual aberration scores. No relationship was found with dissociative experiences scores. Brain activations proceeding and following activation of the right temporo-parietal junction did not correlate with scores on either scale. The positive correlation between performance and right temporo-parietal activation in an own body transformation task with perceptual aberrations scores in our healthy population suggests that disturbances in self- and body processing in individuals along the schizophrenia spectrum might be due to prolonged, rather than stronger activation of the right temporo-parietal junction. We argue that this might reflect local pathology, pathologies in cortico-cortical connections and/or re-entry of top-down processing.

Adult↗

PubMed2006

Metaphor explanation attenuates the right-hand preference for depictive co-speech gestures that imitate actions.

Differential activation levels of the two hemispheres due to hemispheric specialization for various linguistic processes might determine hand choice for co-speech gestures. To test this hypothesis, we compared hand choices for gesturing in 20 healthy right-handed participants during explanation of metaphorical vs. non-metaphorical meanings, on the assumption that metaphor explanation enhances the right hemisphere contribution to speech production. Hand choices were analyzed separately for: depictive gestures that imitate action ("character viewpoint gestures," [McNeill, D. (1992). Hand and mind. What gestures reveal about thought. Chicago: University of Chicago Press.]), depictive gestures that express motion, relative locations, and shape ("observer viewpoint gestures"), and "abstract deictic gestures." It was found that the right-hand over left-hand preference was significantly weaker in the metaphor condition than in the non-metaphor conditions for depictive gestures that imitated action. Findings suggest that the activation of the right hemisphere in the metaphor condition reduces the likelihood of left hemisphere generation of gestures that imitate action, thus attenuating the right-hand preference.

Adult↗

PubMed2006

Neural basis of embodiment: distinct contributions of temporoparietal junction and extrastriate body area.

Embodiment, the sense of being localized within one's physical body, is a fundamental aspect of the self. Recently, researchers have started to show that self and body processing require distinct brain mechanisms, suggesting two posterior brain regions as key loci: the temporoparietal junction (TPJ), which is involved in self processing and multisensory integration of body-related information; and the extrastriate body area (EBA), which responds selectively to human bodies and body parts. Here we used evoked potential mapping and a distributed linear inverse solution to show that activations in EBA and TPJ code differentially for embodiment and self location, because the location and timing of brain activation depended on whether mental imagery is performed with mentally embodied (EBA) or disembodied (TPJ) self location. In a second experiment, we showed that only EBA activation, related to embodied self location, but not TPJ activation, related to disembodied self location, was modified by the subjects' body position during task performance (supine or sitting). This suggests that embodied self location and actual body location share neural mechanisms. Collectively, these data show that distributed brain activity at the EBA and TPJ as well as their timing are crucial for the coding of the self as embodied and as spatially situated within the human body.

Adult↗

PubMed2006

Arm folding, hand clasping, and Luria's concept of "latent left-handedness".

Luria (1947/1970) proposed left-top positions in arm folding (AF) and hand clasping (HC) to be signs of "latent left-handedness". However, research since has revealed that (1) left-top positions are canonical for European right-handers and (2) combined AF/HC measures may provide more information about cerebral laterality than either measure considered alone. We tested whether AF and HC or AF/HC combinations predicted diminished right-handedness for 12 handedness items. Results from 509 healthy participants showed that (1) left-top positions in AF and HC were dominant across participants, as was right-handedness, and a right-top position in HC was associated with attenuated right-handedness, (2) right-hand preference was more frequently associated with congruent AF/HC combinations, especially of the LL type (AF: left-top / HC: left-top), and (3) non-right-hand preference was associated with non-congruent, predominantly LR combinations. We conjecture that the LL type combination indicates left hemispheric dominance for motor actions, whereas the LR combination, in which HC as the distally innervated posture deviates from the canonical pattern, indicates attenuated hemispheric asymmetry. Our data support Luria's proposition that a left-top preference in AF points to "latent" left-handedness, but only if associated with a right-top preference in HC. Consistent left-top preference for the combined AF/HC measure appears to predict right-handedness.

Adolescent↗

PubMed2005

Does contextual information influence positive and negative schizotypy scores in healthy individuals? The answer is maybe.

Defensive responding in schizotypy questionnaires might depend on context. Students completed a schizotypy questionnaire in a "psychiatric" context or a "creativity" context. Positive, but not negative, schizotypy scores were lower in the psychiatry than in the creativity group, but findings applied mainly to male participants. The implications of these findings are critically discussed.

Adolescent↗

PubMed2005

Out-of-body experience, heautoscopy, and autoscopic hallucination of neurological origin Implications for neurocognitive mechanisms of corporeal awareness and self-consciousness.

Autoscopic phenomena (AP) are rare illusory visual experiences during which the subject has the impression of seeing a second own body in extrapersonal space. AP consist of out-of-body experience (OBE), autoscopic hallucination (AH), and heautoscopy (HAS). The present article reviews and statistically analyzes phenomenological, functional, and anatomical variables in AP of neurological origin (n = 41 patients) that have been described over the last 100 years. This was carried out in order to further our understanding of the underlying mechanisms of AP, much as previous research into the neural bases of body part illusions has demystified these latter phenomena. Several variables could be extracted, which distinguish between or are comparable for the three AP providing testable hypotheses for subsequent research. Importantly, we believe that the scientific demystification of AP may be useful for the investigation of the cognitive functions and brain regions that mediate processing of the corporeal awareness and self consciousness under normal conditions.

Awareness↗

PubMed2005

Brain state-dependent functional hemispheric specialization in men but not in women.

Hemispheric specialization is reliably demonstrated in patients with unilateral lesions or disconnected hemispheres, but is inconsistent in healthy populations. The reason for this paradox is unclear. We propose that functional hemispheric specialization in healthy participants depends upon functional brain states at stimulus arrival (FBS). Brain activity was recorded from 123 surface electrodes while 22 participants (11 women) performed lateralized lexical decisions (left hemisphere processing) on neutral and emotional (right hemisphere processing) words. We determined two classes of stable FBS, one with right anterior-left posterior orientations (RA-LP maps) and one with left anterior-right posterior orientations (LA-RP maps). Results show that functional hemispheric specialization is dependent upon the class of FBS and gender. Of those with LA-RP maps, only men showed a strong emotional word advantage (EWA) after left visual field (right hemisphere) presentation, but no EWA after right visual field (left hemisphere) presentation. Subsequent to all other brain states, there was an almost equal EWA after presentation to either visual field. Only about half of the FBS in men led to the pattern of functional hemispheric specialization. We suggest that 'split-brain' research may be marginally describable by a model, but only in exceptional situations, while in connected brains this functional hemispheric specialization is only one of many dynamic states.

Adolescent↗

PubMed2005

Linking out-of-body experience and self processing to mental own-body imagery at the temporoparietal junction.

The spatial unity of self and body is challenged by various philosophical considerations and several phenomena, perhaps most notoriously the "out-of-body experience" (OBE) during which one's visual perspective and one's self are experienced to have departed from their habitual position within one's body. Although researchers started examining isolated aspects of the self, the neurocognitive processes of OBEs have not been investigated experimentally to further our understanding of the self. With the use of evoked potential mapping, we show the selective activation of the temporoparietal junction (TPJ) at 330-400 ms after stimulus onset when healthy volunteers imagined themselves in the position and visual perspective that generally are reported by people experiencing spontaneous OBEs. Interference with the TPJ by transcranial magnetic stimulation (TMS) at this time impaired mental transformation of one's own body in healthy volunteers relative to TMS over a control site. No such TMS effect was observed for imagined spatial transformations of external objects, suggesting the selective implication of the TPJ in mental imagery of one's own body. Finally, in an epileptic patient with OBEs originating from the TPJ, we show partial activation of the seizure focus during mental transformations of her body and visual perspective mimicking her OBE perceptions. These results suggest that the TPJ is a crucial structure for the conscious experience of the normal self, mediating spatial unity of self and body, and also suggest that impaired processing at the TPJ may lead to pathological selves such as OBEs.

Adult↗

PubMed2005

The demystification of autoscopic phenomena: experimental propositions.

Autoscopic phenomena (AP) are rare, illusory visual experiences during which the subject has the impression of seeing a second own body in extrapersonal space. AP consist of out-of-body experience, autoscopic hallucination, and heautoscopy. Recent neurologic reports support the role of multisensory integration deficits of body-related information and vestibular dysfunctions in AP at the temporo-parietal junction. A caveat to test the underlying neurologic and cognitive mechanisms of AP has been their rare and spontaneous occurrence. Recent evidence linked AP to mental own-body imagery engaging brain mechanisms at the temporo-parietal junction. These recent observations open a new avenue for testing AP-related cognitive mechanisms in selected clinical and normal populations. We review evidence on several clinical syndromes (psychosis, depression, anxiety, depersonalization, body dysmorphic disorder), suggesting that some of these syndromes may relate to AP-proneness, thereby leading to testable propositions for future research on body and self processing in addition to AP.

Awareness↗

PubMed2005

Synesthesia: when colors count.

A tacitly held assumption in synesthesia research is the unidirectionality of digit-color associations. This notion is based on synesthetes' report that digits evoke a color percept, but colors do not elicit any numerical impression. In a random color generation task, we found evidence for an implicit co-activation of digits by colors, a finding that constrains neurological theories concerning cross-modal associations in general and synesthesia in particular.

Adult↗

PubMed2005

Psychometric schizotypy modulates levodopa effects on lateralized lexical decision performance.

Emergence of psychotic thought has been related to a breakdown in left-hemisphere language dominance. Dopamine (DA) is implicated in both psychotic pathology and modulation of the semantic system. The present study explored whether controlled DA administration modulates basic language functions: (1) in general and/or (2) as a function of schizophrenia-associated thought. Forty healthy men performed a tachistoscopic lexical decision task. Participants' performance was also analyzed as a function of their positive (magical ideation, MI) and negative (physical anhedonia, PHYSAN) schizotypal features. Half of the subjects received 200 mg levodopa, the other half a placebo. Our findings showed that pharmacological treatment per se did not influence task performance, but influenced laterality patterns as a function of participants' schizotypal features. In the placebo, but not in the levodopa group, right hemisphere language contribution increased as a function of increasing MI scores. In the levodopa, but not in the placebo group, superior left hemisphere lexical decision performance was related to increasing PHYSAN scores. The findings from both substance groups suggest that in the healthy brain, a DA agonist restores left-hemispheric dominance for language by reducing right-hemispheric contribution with respect to a positive schizotypal trait and by increasing left-hemispheric specialization with respect to a negative schizotypal trait. We conjecture that the healthy brain compensates through intact neurochemical mechanisms an increased DA concentration, in particular for persons with elevated positive psychotic-like features.

Adult↗

PubMed2004

Levodopa reverses gait asymmetries related to anhedonia and magical ideation.

Animals and men turn preferentially away from the hemisphere with the more active dopamine (DA) system. Consistent with the idea of a right-hemispheric hyperdopaminergia in schizophrenia, a leftsided turning bias was described for unmedicated psychotic patients. We investigated the modulating role of DA and schizophrenia-like thought on whole-body turns in a controlled double-blind study. The number of veers to either side when walking blindfolded straight ahead (20 meter) was assessed in 40 healthy righthanded men (20 men received levodopa, the remaining participants placebo). Side preferences were analyzed in terms of individuals' positive (Magical Ideation, MI) and negative (Physical Anhedonia, PhysAn) schizotypal features. In the placebo group, increasing MI scores were related to increasing left-sided veering and increasing PhysAn scores were related to increasing right-sided veering. In the levodopa group, this relationship between preferred veering side and type of schizotypy was reversed. The finding in the placebo group suggests an association between MI and a relative right-hemispheric hyperdopaminergia. Unexpectedly, levodopa did not enhance this veering bias, but reversed it, suggesting that psychosis-protective mechanisms exist in the healthy positive "schizotypic" brain. Also unexpectedly, levodopa made "anhedonics" veer like "magics" after placebo, suggesting that DA agonists suppress negative schizotypal symptoms.

Adult↗

PubMed2004

The Ashbya gossypii genome as a tool for mapping the ancient Saccharomyces cerevisiae genome.

We have sequenced and annotated the genome of the filamentous ascomycete Ashbya gossypii. With a size of only 9.2 megabases, encoding 4718 protein-coding genes, it is the smallest genome of a free-living eukaryote yet characterized. More than 90% of A. gossypii genes show both homology and a particular pattern of synteny with Saccharomyces cerevisiae. Analysis of this pattern revealed 300 inversions and translocations that have occurred since divergence of these two species. It also provided compelling evidence that the evolution of S. cerevisiae included a whole genome duplication or fusion of two related species and showed, through inferred ancient gene orders, which of the duplicated genes lost one copy and which retained both copies.

Base Composition↗

PubMed2004

Electrical neuroimaging reveals early generator modulation to emotional words.

Functional electrical neuroimaging investigated incidental emotional word processing. Previous research suggests that the brain may differentially respond to the emotional content of linguistic stimuli pre-lexically (i.e., before distinguishing that these stimuli are words). We investigated the spatiotemporal brain mechanisms of this apparent paradox and in particular whether the initial differentiation of emotional stimuli is marked by different brain generator configurations using high-density, event-related potentials. Such would support the existence of specific cerebral resources dedicated to emotional word processing. A related issue concerns the possibility of right-hemispheric specialization in the processing of emotional stimuli. Thirteen healthy men performed a go/no-go lexical decision task with bilateral word/non-word or non-word/non-word stimulus pairs. Words included equal numbers of neutral and emotional stimuli, but subjects made no explicit discrimination along this dimension. Emotional words appearing in the right visual field (ERVF) yielded the best overall performance, although the difference between emotional and neutral words was larger for left than for right visual field presentations. Electrophysiologically, ERVF presentations were distinguished from all other conditions over the 100-140 ms period by a distinct scalp topography, indicative of different intracranial generator configurations. A distributed linear source estimation (LAURA) of this distinct scalp potential field revealed bilateral lateral-occipital sources with a right hemisphere current density maximum. These data support the existence of a specialized brain network triggered by the emotional connotation of words at a very early processing stage.

Adult↗

PubMed2004

Nonstereotyped responding in positive schizotypy after a single dose of levodopa.

Stereotyped behavior and left-sided orientation biases, associated with the dopamine (DA) system, were observed in populations of the schizophrenia spectrum disorders. We investigated whether heightened DA concentrations influence both side biases and stereotyped responding in a visuo-motor computer task, in which 90, 180, and 270 degrees rotated objects had to be brought into a target position. To account for the role of the schizophrenia spectrum, task performance was also analyzed as a function of healthy participants' high or low magical ideation (MI), a positive schizotypal feature. The first 36 participants (20 women) remained substance free. In a second sample, 20 men received levodopa and 20 men a placebo in a double-blind procedure. Results showed that high MI scorers responded more stereotyped than low MI scorers, without being specifically biased towards the left side. Rotation preferences toward one or the other side made high MI scorers less flexible for objects efficiently to be rotated into the opposite direction. This inflexibility may reflect impaired left hemisphere functioning. Unexpectedly, in the levodopa group, high MI scorers performed superior to low MI scorers. Since DA actions appear to follow an inverted U-shape function, the 'low' performing high MI scorers profited from the enhanced DA availability. Our observation in the levodopa group points to a dissociation between schizotypy and schizophrenia: while cognitive improvement in schizophrenia can occur after treatment with atypical neuroleptic agents, in our positive schizotypal participants a DA agonist resulted in improved task performance. This dissociation may point to protective neurochemical mechanisms preventing healthy schizotypes from developing full-blown psychotic symptoms.

Adult↗

PubMed2003

Human locomotion: levodopa keeps you straight.

Locomotion depends on an intact dopamine system. This system seems to be functionally asymmetric, as evidenced by an asymmetric turning preference. Using a double-blind procedure, the effect of levodopa on the number of veers when walking blindfolded along a straight line (20 m) in the middle of a corridor was tested in 40 healthy dextral men. One group received 200 mg levodopa, while the other group received placebo. We found that (1). subjects veered less after levodopa than after placebo, and (2). improved straight-walking tendency was most prominent for the levodopa group which veered less often to the right side than the placebo group. These findings imply that spatial orientation skills improved under levodopa. We conjecture that a task-dependent dopamine demand during our task was satisfied by levodopa supplementation, and over-proportionately so by the right hemisphere.

Adult↗

PubMed2003

Hands, arms, and minds: interactions between posture and thought.

Based on earlier reports of inconsistent postural preferences in psychiatric populations, we assessed arm folding (AF) and hand clasping (HC) postures in 361 healthy right-handers with different degrees of magical ideation (MI). Subjects generally preferred the congruent combination of a left-arm-top (AF) and a left-thumb-top position (HC). Incongruent subjects, in particular those with a right-arm-top/left-thumb-top position, scored higher on MI than did congruent subjects. Our main finding was thus an association between a style of thinking (MI) and lateral preferences for limb postures, inconsistent across distal (primarily contralaterally innervated) and more proximal (more bilaterally innervated) parts of the body. This association is interpreted in the frame of lesser hemispheric asymmetries in subjects bordering to schizotypal personalities.

Adolescent↗

PubMed2003

Hyperfamiliarity for unknown faces after left lateral temporo-occipital venous infarction: a double dissociation with prosopagnosia.

Right hemisphere dominance in face processing is well established and unilateral right inferior temporo-occipital damage can result in prosopagnosia. Here, we describe a 21-year-old right-handed woman with acute impairment in face recognition that selectively concerned unfamiliar faces, following a focal left lateral temporo-occipital venous infarct. She was severely impaired in discerning that unknown people seen in everyday life were unfamiliar, although she had no difficulty recognizing familiar people. Thus, she had no prosopagnosia, but abnormal 'hyperfamiliarity' for unknown faces. Her difficulty was not accompanied by delusions or deficits in discrimination, identification or memory for faces. Standard neuropsychological testing showed that her recognition of familiar faces was entirely normal. By contrast, her sense of personally knowing faces was severely impaired when unknown faces evoked weak signals of familiarity based on spurious cues, to the extent that she would misattribute fame to faces that were unknown but to which she had been incidentally exposed on a prior occasion. Priming experiments also revealed that, unlike normal subjects, she made familiarity judgements without accessing semantic identity representations. Moreover, in face recognition tests, she generally showed bias in that she relied more on right-hemisphere strategies to identify global traits and less on left-hemisphere processes compared with healthy subjects. This case provides novel evidence for a differential contribution of the two hemispheres to face recognition. Hyperfamiliarity for unknown faces might arise from an imbalance between reciprocal hemispheric functions in face recognition, with relative hypoactivation of left hemisphere processes but hyperactivation of right-hemisphere processes for retrieving stored associations about people, linking seen faces to representations of affective and personal relevance. Hence, abnormal bias in attributing some personal meaning to unknown faces could be evoked by spurious signals of familiarity based on irrelevant affective associations in the right hemisphere.

Adult↗