Blinking and schizotypal thinking

Spontaneous eye blink rate (SBR) is thought to be a biological marker for cerebral dopamine (DA) activity. Accordingly, positive psychotic symptoms have been found to be associated with an increased SBR and negative psychotic symptoms with a decreased SBR. However, modulations of the DA system in patient populations also result from prior neuroleptic treatment. Here, we tested the possible relationship between SBR and positive and negative schizotypal thought. To test the direct influence of DA on SBR in general and as a function of schizotypy, half of a sample of 40 healthy men received levodopa and the other half placebo in a double-blind procedure. SBR did not differ between substance groups suggesting that a pharmacologically induced DA increase in healthy individuals does not generally increase SBR. However, in the levodopa group, increasing SBR correlated with increasing negative schizotypy scores, while no relationship was found between SBR and (1) negative schizotypy in the placebo group, or (2) positive schizotypy in either substance group. We conjecture that a pre-existing hypodopaminergic state in high negative schizotypy scorers, made these individuals susceptible to an increased DA concentration, as it has been observed in Parkinson's disease. Furthermore, the absence of any relationship in the placebo group might suggest that variations in DA concentration as a function of schizotypy are too subtle to influence SBR. Finally, the lack of any association of SBR with positive schizotypy might indicate that SBR and positive schizotypy are mediated by functionally distinct neural circuits.

Human side preferences in three different whole-body movement tasks☆

Animals turn away from the hemisphere with the more active dopamine (DA) system. For humans, a similar relationship has been assumed. However, results from independent studies were obtained from different tasks and indicated different side preferences. To investigate side preferences between different tasks within the same subject, we assessed in 36 healthy research participants (20 women) (1) long-term spontaneous turning (number of 360 degree turns during 20 h), (2) veering (lateral deviations during walking blindfolded straight forward) and (3) stepping (deviations while stepping blindfolded on a given spot) behavior. We observed a left-sided preference for long-term spontaneous turning behavior and no significant side preference for veering and stepping behavior. The absence of consistent side preferences suggests that DA does not equally control lateralized whole-body movements. We propose that visual control enhanced left-sided movement preferences, probably through an enhanced contribution of the right hemisphere to visuo-spatial behavior. Recently, we reported [Neurosci. Lett. 339 (2003) 115] that levodopa supplementation decreases right-sided veering tendencies, while stepping behavior was unaffected by substance intake. We suggest that veering tendencies, which appeared equally pronounced in either direction, are under dopaminergic control as long as attention is directed towards extrapersonal space. Side preferences in lateralized whole-body movement tasks are thus neither comparable between tasks nor within subjects. We conclude that experimental parameters such as visuo-spatial control and spatial task demands (veering is directed to extrapersonal space and stepping to peripersonal space) determine whether or not the DA system is involved.

The effect of aging on postural stability: a cross sectional and longitudinal study

AIMS OF THE STUDY

Only a good knowledge of the effects of age on postural stability allows differentiating between physiological aging and pathologies leading to its impairment. The aims of this study were to define the posturographic parameters which best reflected the effects of aging on postural stability and to determine the slope of postural stability impairment related to aging.

PATIENTS AND METHODS

Postural stability of 50 normal volunteers aged 25-83 years (55.4) was studied with one Kistler force plate. Subjects were asked to stand for 30 s on two-legged stance, eyes open then closed. The center of pressure displacement (COPd) and velocities (COPv), in the antero-posterior (x) and the medio-lateral (z) axis, the sway axis, and the integral of COP displacement vs. time were computed. Eleven subjects were retested at 3 and 6 months to estimate the reliability of posturographic measurements. In addition, 28 subjects aged 25-83 years (60.2) were retested 2.2 years after their first posturographic assessment.

RESULTS

COPxv best reflected postural stability impairment with aging. Closure of the eyes increased the variance of the results. This change was higher in subjects more than 60 years old: 0.019-0.157 cm2 s(-2) than in younger ones: 0.011-0.043 cm2 s(-2). Retesting at 3 and 6 months showed a reliability of 79%. According to the cross-sectional part of the study, the slope of postural stability impairment with aging was estimated at 0.0038 cm/s/year. These results were confirmed by the longitudinal part of the study, which showed that COPxv increased from 0.66-0.75 cm/s/year (P = 0.0001) (slope = 0.0041 cm/s/year).

CONCLUSION

(1) Measurement of COPxv, on two-legged stance, is a simple and reliable way to assess postural stability. (2) Thanks to both a cross sectional and a longitudinal study, the rate of postural stability impairment due to aging was precisely estimated, which will be useful to help distinguishing between the part of postural stability impairment attributable to aging from the one due to neuro-degenerative diseases.

Contralateral medial temporal lobe damage in right but not left temporal lobe epilepsy: a (1)H magnetic resonance spectroscopy study

BACKGROUND

Proton magnetic resonance spectroscopy (MRS) of the hippocampus is useful in lateralising the epileptic focus in temporal lobe epilepsy for subsequent surgical resection. Previous studies have reported abnormal contralateral MRS values in up to 50% of the patients.

OBJECTIVE

To identify the contributing factors to contralateral damage, as determined by MRS, and its extension in patients with temporal lobe epilepsy.

METHODS

Single voxel MRS was carried out in the hippocampus and lateral temporal neocortex of both hemispheres in 13 patients with left temporal lobe epilepsy (LTLE) and 16 patients with right temporal lobe epilepsy (RTLE). All patients had mesial temporal lobe epilepsy with hippocampal sclerosis. Controls were 21 healthy volunteers of comparable age.

RESULTS

Consistent with previous studies, the NAA/(Cho+Cr) ratio was abnormally low in the hippocampus ipsilateral to the focus (p < 0.0001), and there were lower values in both patient groups in the ipsilateral temporal neocortex (p < 0.0001). Patients with RTLE had left hippocampal MRS anomalies (p = 0.0018), whereas the right hippocampus seemed to be undamaged in LTLE patients.

CONCLUSIONS

Unilateral mesial temporal lobe epilepsy is associated with widespread metabolic abnormalities which involve contralateral mesial and neocortical temporal lobe structures. These abnormalities appear to be more pronounced in patients with RTLE.

"Tumor-mimicking" multiple sclerosis

The spectrum of clinical manifestations of multiple sclerosis (MS) may include rare cases where cerebral lesions simulate brain tumors or abscesses on neuroimaging. We report here on a 43-year-old woman with numerous ring-enhancing cystic lesions in the white matter of cerebral hemispheres, brainstem and cerebellum. The radiological picture was overwhelmingly in favor of a metastatic or infectious etiology, but brain biopsy showed subacute demyelination with central necrosis.

Pure global acalculia following a left subangular lesion

We describe the case of a right-handed patient who presented a severe acalculia in the context of a pure Gerstmann syndrome following a subangular lesion that spared the left inferior parietal lobule (IPL). The patient showed impairments in Arabic and verbal codes, in number production and comprehension, as well as in numerical facts and problem solving. By using the EC301 calculation battery, semantic and syntactic tasks in Arabic and verbal codes, we tested the different hypotheses raised by the cognitive neuropsychological models of acalculia. The patients' difficulties, which were not associated with a general intellectual deterioration, and those affecting number processing as a particular semantic class, were indicative of a "global acalculia". This deficit, which exceeded the anarithmetia usually described in Gerstmann syndrome following left IPL lesion, suggested that the isolation of this area may constitute a sufficient condition for producing such a global acalculia. These results are discussed in terms of a disorder in the manipulation of mental images of spatially related objects.

Dog phobia in a motion-blind patient

INTRODUCTION

A prominent neurophysiological model of phobia generation holds that specific phobia might result from the uncoupling of unaware subcortical fear responses from aware cortical fear responses. Former responses are thought to be automatic and fast, providing approximate information about the external stimulus, whereas the latter responses are more controlled and allow comparison with previous experience. Since only the cortical pathway carries information available to awareness, this model also accounts for the striking irrationality of specific phobia in humans.

METHODS

Here, we report neuropsychological and neuro-ophthalmological findings in a 41-year-old patient who developed severe dog phobia following bilateral parietal lobe damage.

RESULTS

The examinations showed a severe deficit in visual motion perception (visual motion blindness or akinetopsia) as well as spatial vision. Importantly, the patient was largely unaware of his visual deficits.

CONCLUSION

Based on the present observation it is argued that irrational fear, as found in specific phobia, might not only result from a general uncoupling of aware cortical from unaware subcortical fear responses, but also from a functionally similar dissociation at the cortical level.

Pure imagery hemi-neglect of far space

Patients with hemispatial neglect restricted to near (within reaching distance) or to far space (beyond reaching distance) have been described. This constitutes a double-dissociation considered by current neurocognitive thinking as compelling evidence for separate networks. However, a similar double-dissociation exists with respect to perceived as opposed to imagined space. If the organization of represented space was similar to that of perceived space, it should contain a far/near dissociation as well. This paper describes a patient with pure representational neglect restricted to far space.

Opposite Turning Behavior in Right-Handers and Non-Right-Handers Suggests a Link Between Handedness and Cerebral Dopamine Asymmetries

The strong right hand preference in humans remains a riddle; no lateralized behavior other than fine finger dexterity relates to it. The relation between handedness and language dominance may be far weaker than currently judged; after all, both right-handers and non-right-handers utilize the left brain for speech. There is, however, a lateralized motor preference in animals, turning behavior, that is strongly associated with hemispheric dopamine (DA) asymmetries. Turning consistently occurs towards the side with less DA. The authors tested 69 right-handers and 24 non-right-handers with a device recording spontaneous turning behavior for 20 hr within 3 days. Findings indicate that right-handers preferred left-sided turning and non-right-handers preferred right-sided turning. This result suggests a link between handedness and DA asymmetries.

Neuropathology of a case of dopa-responsive dystonia associated with a new genetic locus, DYT14

Detailed autopsy findings are reported for a patient with dopa-responsive dystonia genetically related to the dopa-responsive dystonia locus DYT14 on chromosome 14q13. Substantia nigra and locus ceruleus showed a normal abundance of severely hypomelanized dopaminergic neurons and no Lewy body. In the nigra, the reduction of melanin pigment was found to be asymmetric between the two sides and uneven within neurons, and the lateral aspect of the nigra appeared more affected than the medial, in a pattern similar to the neuronal loss in PD. Dopa-responsive dystonia has a unique neuropathologic signature that seems to be independent of its genotype.

Noninvasive localization of electromagnetic epileptic activity. I. Method descriptions and simulations

This paper considers the solution of the bioelectromagnetic inverse problem with particular emphasis on focal compact sources that are likely to arise in epileptic data. Two linear inverse methods are proposed and evaluated in simulations. The first method belongs to the class of distributed inverse solutions, capable of dealing with multiple simultaneously active sources. This solution is based on a Local Auto Regressive Average (LAURA) model. Since no assumption is made about the number of activated sources, this approach can be applied to data with multiple sources. The second method, EPIFOCUS, assumes that there is only a single focal source. However, in contrast to the single dipole model, it allows the source to have a spatial extent beyond a single point and avoids the non-linear optimization process required by dipole fitting. The performance of both methods is evaluated with synthetic data in noisy and noise free conditions. The simulation results demonstrate that LAURA and EPIFOCUS increase the number of sources retrieved with zero dipole localization error and produce lower maximum error and lower average error compared to Minimum Norm, Weighted Minimum Norm and Minimum Laplacian (LORETA). The results show that EPIFOCUS is a robust and powerful tool to localize focal sources. Alternatives to localize data generated by multiple sources are discussed. A companion paper (Lantz et al. 2001, this issue) illustrates the application of LAURA and EPIFOCUS to the analysis of interictal data in epileptic patients.

Direction-specific motion blindness induced by focal stimulation of human extrastriate cortex

Motion blindness (MB) or akinetopsia is the selective disturbance of visual motion perception while other features of the visual scene such as colour and shape are normally perceived. Chronic and transient forms of MB are characterized by a global deficit of direction discrimination (pandirectional), which is generally assumed to result from damage to, or interference with, the motion complex MT+/V5. However, the most characteristic feature of primate MT-neurons is not their motion specificity, but their preference for one direction of motion (direction specificity). Here, we report that focal electrical stimulation in the human posterior temporal lobe selectively impaired the perception of motion in one direction while the perception of motion in other directions was completely normal (unidirectional MB). In addition, the direction of MB was found to depend on the brain area stimulated. It is argued that direction specificity for visual motion is not only represented at the single neuron level, but also in much larger cortical units.

[Variability of right hemisphere activation during semantic word processing in aphasic patients: an electrophysiologic study in three patients]

After stroke, the interhemispheric reorganisation of the neural network implicated in language is hypothesized to be a function not only of the site of lesion but also of the residual impairment. With a multiple case approach, we tested this hypothesis in three chronic aphasic patients. Two patients, GE (capsulo-lenticular stroke) and JHN (fronto-temporal stroke) showed formal residual semantic difficulties, while the third patient (EG, large sylvian lesion) did not. Brain electric activity was analysed during a categorisation task of tachistoscopically presented words in the left and the right visual field. The temporal analysis of brain activity showed that both patients with semantic residual difficulties activated the right hemisphere (RH) during some steps of word processing. In the third patient, without semantic impairment, the RH was activated only during a short time period. Further more, RH activation was shown to be dependent on the visual field of word presentation. Phonological impairment was not predictive of RH activation. These results suggest that RH activation, particularly anterior regions, can occur during semantic processing of words as a function of semantic residual impairment.

Beneficial effect of co-polymer 1 on cytokine production by CD4 T cells in multiple sclerosis

Multiple sclerosis (MS) has been associated with an imbalance in the T helper type 1 (Th1) and Th2 subsets. We investigated, at the single-cell level, the synthesis of pro-inflammatory cytokines by CD4 and CD8 T cells from MS patients. We report the relationship between priming of CD4 and CD8 T cells for interleukin-2 (IL-2), interferon-gamma (IFN-gamma) and tumour necrosis factor-alpha (TNF-alpha) and disease evolution in MS patients, clinically subdivided into relapsing-remitting MS (RRMS) in remission, RRMS in relapse, or chronic progressive MS (CPMS). Moreover, we report the in vivo influence of co-polymer 1 (COP) treatment on the pattern of cytokine producers in RRMS patients. We show that the frequency of CD4 T cells primed for TNF-alpha synthesis increased in all stages of MS, including RRMS remitting, and was normalized to control values in COP-treated patients (43.2 +/- 11.8% in treated patients versus 47 +/- 7.3% in RRMS remitting versus 40.3 +/- 8% in controls). In addition, a significant decrease in the frequency of CD4 T cells primed for IL-2 was found in COP-treated patients as compared to the other groups of patients, reaching values below that of controls (59.1 +/- 9.9% in treated patients versus 70 +/- 11.6% in RRMS remitting versus 67.1 +/- 7.4% in controls). Unexpectedly, COP-treated patients also showed a significantly decreased priming for IFN-gamma at the CD4 T-cell level (9.1 +/- 3.4% in treated patients versus 18.8 +/- 0.6.4% in RRMS remitting versus 15.4 +/- 4.7% in controls), but not at the CD8 T-cell level. This bystander suppression on the inflammatory cells should be considered in the monitoring of MS patients submitted to COP treatment, in order to evaluate better its clinical efficacy.

So near yet so far: neglect in far or near space depends on tool use

The study of unilateral spatial neglect has shown that space can be dissociated on a peripersonal versus extrapersonal basis. We report a novel type of dissociation based on tool use in a patient suffering from left neglect. Line bisection was carried out in near and far space, using a stick and a laser pointer. A rightward bias was always found for the former, but not for the latter. Neglect thus appears to be contingent not only on distance, but also on the motor action required by the task.

Intracranial Neurophysiological Correlates Related to the Processing of Faces

Face perception and recognition is an intriguing ability, already present in neonates. Numerous studies in patients with brain lesions identified the temporo-occipital cortex as the crucial structure for this capacity. Analysis of electrical signals (EEG) inside the brain of patients implanted with intracranial electrodes for diagnostic purposes allows researchers to describe the temporal and spatial organization of responses to various aspects of face processing in human subjects. Several findings have emerged and appear relevant for cerebral organization in general: (1) Selective face responses were obtained from the basal temporo-occipital cortex at around 200 ms (N200); however, other structures such as the lateral temporal lobe and frontal cortex also participate in face recognition and perception tasks. (2) Each structure has a distinct "response profile"; that is, with respect to a given task certain structures respond strongly, others less or not at all. This profile might change with a different task, although the physical parameters of the stimuli remain the same. (3) The right hemispheric predominance of face processing, as suggested by patient data and studies in healthy volunteers, seemed to be restricted to its early stages (i.e., before 100-150 ms). (4) Recognition of faces might be associated with differential intracranial responses, despite an incorrect overt response, reflecting neurophysiological correlates of implicit memory. (5) The more the stimulus resembled a complete human face, the earlier and larger the N200 response was found, in particular over the basal temporobasal cortex. Analysis of electrical signals from intracranial electrodes might help to improve our understanding of the underlying physiological and anatomical constraints of cognitive processes.

Electric source imaging of human brain functions

We review recent methodological advances in electromagnetic source imaging and present EEG data from our laboratory obtained by application of these methods. There are two principal steps in our analysis of multichannel electromagnetic recordings: (i) the determination of functionally relevant time periods in the ongoing electric activity and (ii) the localization of the sources in the brain that generate these activities recorded on the scalp. We propose a temporal segmentation of the time-varying activity, which is based on determination of changes in the topography of the electric fields, as an approach to the first step, and a distributed linear inverse solution based on realistic head models as an approach to the second step. Data from studies of visual motion perception, visuo-motor transfer, mental imagery, semantic decision, and cognitive interference illustrate that this analysis allows us to define the patterns of electric activity that are present at given time periods after stimulus presentation, as well as those time periods where significantly different patterns appear between different stimuli and tasks. The presented data show rapid and parallel activation of different areas within complex neuronal networks, including early activity of brain regions remote from the primary sensory areas. In addition, the data indicate information exchange between homologous areas of the two hemispheres in cases where unilateral stimulus presentation requires interhemispheric transfer.

Pure representational neglect after right thalamic lesion

After a right thalamic stroke, an 86-year-old man presented an acute pure left representational neglect in the absence of any perceptual neglect. On spatial mental imagery tasks, the patient systematically omitted items located on his left side, but only when a vantage point was given. This suggests that (1) pure representational neglect is not just a residual finding after recovery from global (perceptual and representational) neglect; (2) space representation can be coded by two independent processes: in viewer-centered or world-based (allocentric) coordinates; and (3) the right thalamus serves as a relay in the processing of spatial visual imagery.

Associations to smell are more pleasant than to sound

To assess and compare the quantitive and qualitative aspects of verbal associations of olfaction and audition, we conducted two verbal category fluency tasks, one consisting of the generation of 'smelling' associations and the other of 'auditory' associations. The responses of the 40 subjects on these fluency tasks were rated as pleasant or unpleasant by themselves as well as by an independent group of 40 subjects. In addition, all 80 healthy, right-handed subjects rated their momentary emotional state on a visual analog scale. The mean number of words generated by the 40 subjects did not differ between the two tasks, and in both tasks pleasant associations were more frequent than unpleasant associations. However, for all subjects, the proportion of pleasant associations was significantly higher in the olfactory compared to the auditory fluency task. The finding of more pleasant associations in both tasks confirms previous reports, but the pronounced effect in the olfactory task suggests that odors may be more hedonically coded than other sensory modalities, i.e., audition. Although there is evidence that the majority of odors are initially perceived as unpleasant, when retrieved from memory, pleasant connotations seem to dominate. The possible mechanisms for this dissociation are discussed.