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1.
Cannabis abuse may precipitate the onset of schizophrenia and a dysfunction of the endocannabinoid system may be involved in the pathology of schizophrenia. Nevertheless, only few studies have addressed the neurobiological consequences of cannabis abuse for the development and course of schizophrenia. We measured the long-term effect of chronic cannabis abuse on the inhibitory function of the brain by the auditory P50 sensory gating in schizophrenic (n=15) and otherwise healthy chronic cannabis abusers (i.e. cannabis controls; n=11) and compared it to that of schizophrenic patients (n=12) and healthy controls (n=18) without cannabis or other drug abuse. All study subjects had to be abstinent from cannabis for at least 28 days. The main finding of our study was a P50 sensory gating deficit in cannabis controls that was correlated with the number of years with daily consumption (r=0.81; p=0.003). In contrast, we found no differences in P50 sensory gating between schizophrenic cannabis-abusers and non-abusers or healthy controls and no correlation with the number of years with daily consumption in those groups. To our knowledge this is the first study comparing the influence of chronic cannabis abuse in schizophrenic and otherwise healthy abusers on the inhibitory function of the brain. Our data provide some evidence that chronic cannabis abuse may affect sensory cortical circuits even after prolonged abstinence and they point to a possible differential effect in schizophrenic and otherwise healthy users.  相似文献   
2.
Varying degrees of neurologic function spontaneously recovers in humans and animals during the days and months after spinal cord injury (SCI). For example, abolished upper limb somatosensory potentials (SSEPs) and cutaneous sensations can recover in persons post-contusive cervical SCI. To maximize recovery and the development/evaluation of repair strategies, a better understanding of the anatomical locations and physiological processes underlying spontaneous recovery after SCI is needed. As an initial step, the present study examined whether recovery of upper limb SSEPs after contusive cervical SCI was due to the integrity of some spared dorsal column primary afferents that terminate within the cuneate nucleus and not one of several alternate routes. C5-6 contusions were performed on male adult rats. Electrophysiological techniques were used in the same rat to determine forelimb evoked neuronal responses in both cortex (SSEPs) and the cuneate nucleus (terminal extracellular recordings). SSEPs were not evoked 2 days post-SCI but were found at 7 days and beyond, with an observed change in latencies between 7 and 14 days (suggestive of spared axon remyelination). Forelimb evoked activity in the cuneate nucleus at 15 but not 3 days post-injury occurred despite dorsal column damage throughout the cervical injury (as seen histologically). Neuroanatomical tracing (using 1% unconjugated cholera toxin B subunit) confirmed that upper limb primary afferent terminals remained within the cuneate nuclei. Taken together, these results indicate that neural transmission between dorsal column primary afferents and cuneate nuclei neurons is likely involved in the recovery of upper limb SSEPs after contusive cervical SCI.  相似文献   
3.
OBJECTIVE: Alexithymia has a high prevalence in patients with chronic or somatoform pain disorders. Various investigations demonstrated a hypersensitivity and low tolerance of alexithymics to touch and painful stimulation. It was argued that alexithymic characteristics may lead an individual to augment stimuli in order to prevent ignoring stimuli that might be dangerous. Therefore, there may be a relation to the reducer-augmenter construct. To test this hypothesis, cortical reactivity in response to unpleasant acoustical stimulation was measured. METHODS: Nineteen high alexithymics and 18 low alexithymics were stimulated with five series of acoustic stimuli (white noise) of different intensity levels. Evoked potentials were recorded at electroencephalogram electrodes Fz, Cz, and Pz. RESULTS: With ascending stimulus intensities, both groups showed increasing P1-N1 and N1-P2 peak-to-peak amplitudes. High alexithymics had higher P1-N1 amplitudes and a stronger intensity-dependent slope of P1-N1 amplitude. In contrast to that, N1-P2 amplitude of low alexithymics tended to decrease in response to the highest stimulus intensity level. CONCLUSION: High alexithymic subjects seem to behave like cortical augmenters. This may be due to a disturbed transmarginal inhibition, which may normally serve as a protective physiological mechanism.  相似文献   
4.
Lawson AL  Guo C  Jiang Y 《Neuropsychologia》2007,45(6):1223-1231
The effects of age on repetition priming and how such differences were related to intentional learning and working memory status were examined. Fourteen older (age 65-75) and 14 younger (age 18-28) healthy adults performed a modified delayed match-to-sample task consisting of a target object held in mind followed by nine test objects. Sixty four-channel EEGs were recorded as participants indicated whether each test object was the same or different from the target object. Half of all target and distractor objects were intentionally studied prior to the task, and both target and distractor objects were repeatedly presented up to four times in each trial. Although both age groups showed repetition priming effects, speed increases due to repetition were more enhanced for elderly. ERP repetition effects for both younger and older adults were indexed via early (200-550) and late (550-850 ms) components. The early repetition effect was affected by whether a distractor was previously studied or not for younger but not for older adults. In contrast, the late repetition effect was not affected by prior intentional learning, and a marginal age effect suggested that repetitions of distractors likely affected older and younger adults differently. These findings suggest that at least two distinguishable repetition mechanisms differentially affect adult aging.  相似文献   
5.
Little is known about the initial stages of information processing in amnesia as compared to normal memory. In this study, we used electrical spatiotemporal mapping to compare cortical activation during encoding and recognition in a 56-year-old patient with severe, chronic post-anoxic amnesia and an age-matched control group. Event-related potentials were recorded as the subjects performed a continuous recognition task composed of meaningful designs. Activation in the control group rapidly progressed through eight different electrocortical configurations over 700 ms after onset of new stimuli. In contrast, activation in the amnesic patient was highly monotonous: it showed varying electrocortical patterns only during the first 150 ms but then remained abnormally stable for the remainder of the analysed time window. Electrical source localisation revealed that the patient failed to activate distributed cortical networks and that his processing was confined to visual areas. The present study suggests that the rapid activation of distributed cortical networks is critical for efficient encoding.  相似文献   
6.
Conty L  N'Diaye K  Tijus C  George N 《Neuropsychologia》2007,45(13):3024-3037
Direct gaze or eye contact is a strong social signal, which triggers distinct processes as compared to other gaze directions. Thus, direct gaze could be early dissociated from averted gaze during the processing of gaze direction. In order to examine the processing of gaze contact relative to averted gaze, we studied evoked potentials in human adults in response to the apparent motion of gaze. Deviated and frontal faces were presented with a fixed gaze direction, followed by an apparent movement of the eyes either toward the subject or away from him/her. The results showed that the perception of direct relative to averted gaze evoked a greater, later and longer lasting N170, suggesting that gaze contact recruited more resources than averted gaze in the early stage of gaze direction processing. Furthermore, direct and averted motion of gaze elicited distinct ERP components between 160 and 210 ms, initiated over centro-parietal electrodes. Source reconstruction revealed the involvement of the Theory-of-Mind network, including the regions of the superior temporal sulcus, the medial prefrontal and the orbitofrontal cortices, in this early dissociation. In addition, the perception of gaze contact relative to averted gaze yielded increased fronto-central P3a and parieto-occipital P3b. All the results were significant whatever the head orientation. Our findings show that gaze contact, as compared to other gaze directions, is an essential social cue which recruits early specific processes. The dissociation between direct and averted gaze processing occurs as soon as 160 ms, involving the social brain network.  相似文献   
7.
Summary. In Alzheimer’s disease (AD), mild functional disturbances should precede gross structural damage and even more clinical symptoms, possibly by decades. Moreover, alterations in the brainstem are supposed to occur earlier as cortical affections. Based on these considerations, we developed a new method aiming at the measurement of vagal brainstem functioning by means of evoked potentials after electrical stimulation of the cutaneous representation of the vagus nerve in the external auditory channel. In the current study, a first sample of patients with Alzheimer’s disease (n = 7) and mild cognitive impairment (n = 3) were investigated (6m, 4f, range from 57 to 78 y, mean age 68.6 years). Vagus somatosensory evoked potentials (VSEP) were characterized by significantly longer latencies as compared to healthy age- and gender-matched controls (p < 0.05). Future large scale studies – also including preclinical stages of AD – have to assess the value of this non-invasive, fast and cheap method in the early diagnosis of neurodegenerative disorders.  相似文献   
8.
Summary A traditional view has been that balance control occurs at a very automatic level, primarily involving the spinal cord and brainstem; however, there is growing evidence that the cerebral cortex and cognitive processing are involved in controlling specific aspects of balance. The purpose of this review is to summarize recent literature pertaining to the cognitive demands and cortical control of balance-recovery reactions, focussing on five emerging sources of evidence: 1) dual-task studies demonstrating that concurrent performance of cognitive and balance-recovery tasks leads to interference effects; 2) dual-task studies that have examined the temporal dynamics associated with the reallocation of cognitive resources to the balance-recovery task; 3) visual attention studies that have inferred contributions of visual attention based on gaze measurements and/or manipulations to occlude vision; 4) measurements of brain potentials evoked by postural perturbation; and 5) use of transcranial magnetic stimulation to alter contributions from specific cortical areas.  相似文献   
9.
In median nerve somatosensory evoked potentials, the cortical N35 amplitude sometimes exceeds the P25 amplitude (C3’/C4’ referred to Fz; “enhanced N35” feature). Six hundred consecutive patient median nerve SEPs were retrospectively analysed and compared with 27 controls. The feature was more often present in patients with dystonia (62%) than in patients with other disorders (22%; relative risk for the condition 2.8; Fisher’s exact p = 0.003) or control subjects (7.4%; odds ratio 20; p = 0.0006). Similarly, the feature was more often present in patients with myoclonus (38%) than in patients with other disorders (22%; relative risk 1.7; p = 0.02) or control subjects (odds ratio 7.5; p = 0.006).There was no clear relationship of the feature to short latency SEP abnormalities except in cases of myoclonus. Further comparison was made of the characteristics of 72 patients each, with and without the feature, whose short latency SEP components were normal. The relationship of the feature to dystonia or myoclonus held true in this case-controlled arm of the study. The sensitivity and specificity were 65% and 78% respectively for any form of dystonia; 43% and 79% respectively for any form of myoclonus. The feature was even more specific in both conditions when compared with controls (93%). Most cases of dystonia with an identifiable cause in this study were of secondary forms. It is known that this feature often occurs in association with “giant” SEPs in some myoclonic conditions. However, its occurrence in dystonia may be a useful new finding in an established test, helping to identify a condition where there is increasing evidence for disordered sensorimotor integration. Received in revised form: 13 January 2006  相似文献   
10.
We used Motor Evoked Potentials (MEPs), elicited by transcranial magnetic stimulation, for assessing a motor pathways dysfunction in a selected group of Multiple Sclerosis (MS) patients, without limitation in walking. We selected 32 Relapsing Remitting MS patients, in remission phase, with EDSS ≤ 3.5 and 20 healthy individuals with similar height and age distribution. We measured the following MEP parameters: motor thresholds; central motor conduction time (CMCT); amplitude and area, both expressed as MEP/CMAP ratio. Patients were divided into two groups according to the EDSS score: non-disabled group (ND; EDSS 0–1.5) and disabled group (D; EDSS 2–3.5). Mean average MEP values were significantly different in the patients compared with the controls. Even in MS patients with no or minor neurological signs (ND group), MEP parameters showed differences from controls and furthermore all MEP parameters were significantly different in the D group compared with the ND group. The 75% of the patients had an amplitude or area alteration; this percentage was significantly higher than the percentage of patients with a CMCT alteration (56.2%). In addition, CMCT increase was always associated with reduced amplitude and area, but amplitude and area alterations were present also in patients with normal CMCT. In early stages of MS, the higher percentage shown in alteration of MEP amplitudes and areas as opposed to CMCTs has not previously been highlighted in the literature. Independently of its pathogenesis (demyelination or axonal loss), the amplitude or area decrease should be considered in clinical trials and in follow-up studies, as a marker of the motor pathways dysfunction, at least as much as CMCT increase. Received in revised form: 3 April 2006  相似文献   
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