Neuroscience letters
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Neuroscience letters · Feb 2013
Impaired cerebral glucose metabolism in prodromal Alzheimer's disease differs by regional intensity normalization.
Using [(18)F] fluorodeoxyglucose (FDG) positron emission tomography (PET) patients with Alzheimer's disease show impairment of cerebral glucose metabolism in bilateral frontotemporoparietal association cortices and posterior cingulate cortex whereas in patients with mild cognitive impairment (MCI) results are heterogeneous. For the first time, the present study examined alterations of the cerebral glucose metabolism in patients with prodromal AD as compared to patients with AD dementia and healthy controls depending on intensity normalization. 15 patients with AD (69.8±8.5 years) and 28 with prodromal AD (67.4±9.1 years) as well as 10 healthy controls (58.8±5.9 years) underwent FDG PET under resting conditions. By statistical parametric mapping 8, analyses were performed using (a) cerebellar cortex or (b) whole brain as reference region for intensity normalization. ⋯ By contrast, patients with prodromal AD had only reductions in the left posterior temporal lobe and left angular gyrus as compared with controls. Cerebellar normalization was superior in differentiating patients with prodromal AD or AD dementia from healthy controls, but global normalization provided slightly better contrasts for the differentiation between patients with prodromal AD and AD dementia in AD-typical regions. Unexpected hypermetabolism in patients was only revealed using global normalization and has to be regarded as an artifact of intensity normalization to a reference region affected by the disease.
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Neuroscience letters · Feb 2013
Transcranial direct current stimulation (tDCS) priming of 1Hz repetitive transcranial magnetic stimulation (rTMS) modulates experimental pain thresholds.
Transcranial direct current stimulation (tDCS) and repetitive transcranial magnetic stimulation (rTMS) of primary motor cortex (M1) modulate cortical excitability. Both techniques have been demonstrated to modulate chronic pain and experimental pain thresholds, but with inconsistent effects. Preconditioning M1 with weak tDCS (1mA) standardizes the effects of subsequent stimulation via rTMS on levels of cortical excitability. ⋯ Cathodal tDCS preconditioning of 1Hz rTMS successfully reversed the normal suppressive effect of low frequency rTMS and effectively modulated cold and heat pain thresholds. Conversely, anodal tDCS - 1Hz rTMS led to a decrease in cold pain thresholds. Therefore, this study supports that preconditioning M1 using cathodal tDCS before subsequent stimulation via 1Hz rTMS facilitates the production of analgesia.
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Neuroscience letters · Feb 2013
The effects of menthol on cold allodynia and wind-up-like pain in upper limb amputees with different levels of phantom limb pain.
The mechanisms underlying phantom limb pain are not fully known, but hypersensitivity appears to be a central element. Menthol has previously been suggested as a model for hypersensitivity, but it has not yet been investigated if different levels of neuropathic pain may influence the effects of menthol or if topical application of menthol may act as a model for hypersensitivity in patients with phantom limb pain. In the present study, menthol (l-menthol 40%) was applied to the affected and non-affected sides in 24 upper-limb amputees with different levels of phantom limb pain to test if menthol could induce cold allodynia and exacerbate wind-up-like pain. ⋯ After application of menthol, the level of phantom limb pain was only related to wind-up-like pain following brush (P=0.011) but not pinprick stimulation (P=0.233). This study indicates that menthol does influence hypersensitivity in phantom limb pain patients, and it is the first study to show that menthol may exacerbate wind-up-like pain in this group of neuropathic pain patients. The findings suggest that menthol may act as a model for studying sensitization in phantom limb patients.
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Neuroscience letters · Feb 2013
Involvement of central cholinergic mechanisms on sodium intake induced by gabaergic activation of the lateral parabrachial nucleus.
Bilateral injections of the GABA(A) agonist muscimol into the lateral parabrachial nucleus (LPBN) disrupt satiety and induce strong ingestion of water and 0.3M NaCl in fluid-replete rats by mechanisms not completely clear. In the present study, we investigated the effects of the blockade of central muscarinic cholinergic receptors with atropine injected intracerebroventricularly (i.c.v.) on 0.3M NaCl and water intake induced by muscimol injections into the LPBN in fluid-replete rats. Male Holtzman rats with stainless steel cannulas implanted bilaterally into the LPBN and unilaterally into the lateral ventricle (LV) were used. ⋯ The i.c.v. injection of atropine did not affect 0.3M NaCl (26.8±6.2mL/2h, vs. saline i.c.v.: 36.5±9.8mL/2h) or water intake (14.4±2.5mL/2h, vs. saline i.c.v.: 15.6±4.8mL/2h) in rats treated with furosemide+captopril subcutaneously combined with bilateral injections of moxonidine (α(2)-adrenoceptor/imidazoline agonist, 0.5nmol/0.2μL) into the LPBN, suggesting that the effect of atropine was not due to non-specific inhibition of ingestive behaviors. The results show that active central cholinergic mechanisms are necessary for the hypertonic NaCl and water intake induced by the blockade of the inhibitory mechanisms with injections of muscimol into the LPBN in fluid-replete rats. The suggestion is that in fluid-replete rats the action of LPBN mechanisms inhibits facilitatory signals produced by the activity of central cholinergic mechanisms to maintain satiety.
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Neuroscience letters · Feb 2013
Pragmatic inferences modulate N400 during sentence comprehension: evidence from picture-sentence verification.
The present study examines the online realization of pragmatic meaning using event-related potentials (ERPs). Participants read sentences including the English quantifier some, which has both a semantic meaning (at least one) and a pragmatic meaning (not all). ⋯ ERPs at the object word, which determined whether the sentence was consistent with the story, showed the largest N400 effect for objects that made the sentence false, whereas they showed an intermediate effect for objects that made the sentence false under the pragmatic interpretation but true under the semantic interpretation. The results suggest that this pragmatic aspect of meaning is computed online and integrated into the sentence model rapidly enough to influence comprehension of later words.