Biomedical subjects

C J Ploner

Publications and source records attributed to C J Ploner.

24 records · Page 2Linked to original sources

PubMed1998

Effects of repetitive transcranial magnetic stimulation over dorsolateral prefrontal and posterior parietal cortex on memory-guided saccades.

We investigated the role of the dorsolateral prefrontal cortex (DLPFC) and the posterior parietal cortex (PPC) in a visuospatial delayed-response task in humans. Repetitive transcranial magnetic stimulation (20 Hz, 0.5 s) was used to interfere temporarily with cortical activity in the DLPFC and PPC during the delay period. Omnidirectional memory-guided saccades with a 3-s delay were used as a quantifiable motor response to a visuospatial cue. The question addressed was whether repetitive transcranial magnetic stimulation (rTMS) over the DLPFC or PPC during the sensory of memory phase affects accuracy of memory-guided saccades. Stimulation over the primary motor cortex served as control. Stimulation over the DLPFC significantly impaired accuracy of memory-guided saccades in amplitude and direction. Stimulation over the PPC impaired accuracy of memory-guided saccades only when applied within the sensory phase (50 ms after cue offset), but not during the memory phase (500 ms after cue offset). These results provide further evidence for a parieto-frontal network controlling performance of visuospatial delayed-response tasks in humans. It can be concluded that within this network the DLPFC is mainly concerned with the mnemonic representation and the PPC with the sensory representation of spatially defined perceptual information.

Adult↗

PubMed1998

Cortical control of saccades.

Saccadic eye movements are controlled by a cortical network composed of several oculomotor areas that are now accurately localized. Clinical and experimental studies have enabled us to understand their specific roles better. These areas are: (1) the parietal eye field (PEF) located in the intraparietal sulcus involved in visuospatial integration and in reflexive saccade triggering; (2) the frontal eye field (FEF), located in the precentral gyrus, involved in the preparation and the triggering of purposive saccades; and (3) the supplementary eye field (SEF) on the medial wall of the frontal lobe, probably involved in the temporal control of sequences of visually guided saccades and in eye-hand coordination. A putative cingulate eye field (CEF), located in the anterior cingulate cortex, would be involved in motivational modulation of voluntary saccades. Besides these motor areas, the dorsolateral prefrontal cortex (dlPFC) in the midfrontal gyrus is involved in reflexive saccade inhibition and visual short-term memory.

Cerebral Cortex↗

PubMed1998

Temporal limits of spatial working memory in humans.

An essential feature attributed to working memory is the labile and transient nature of its representations. Using an oculomotor task, we examined the stability of spatial working memory in 16 normal human subjects. Eye movements towards remembered spatial cues (memory-guided saccades) were electro-oculographically recorded after memorization delays that varied unpredictably between 0.5 and 30s. A peaked time-course of saccadic targeting errors, with maximal errors around 20s delay, was found, showing that delay-dependent decay of spatial information in working memory occurs, but is time-limited and reverts significantly beyond delays of about 20s. These data (i) indicate temporal limits of spatial working memory and (ii) provide the first behavioural evidence for the existence of two parallely generated mental representations of space that successively control memory-guided behaviour in humans.

Adult↗

PubMed1997

[Repetitive transcranial magnetic stimulation. Possibilities, limits and safety aspects].

Repetitive magnetic stimulation (rTMS) is a non-invasive, painless method to induce transient activation in circumscript regions of the human cortex. In contrast to TMS with single pulses rTMS allows a more effective stimulation of association cortex and temporary interference with the proper functioning of stimulated areas. Possible applications for examination of the functional anatomy of language lateralisation, memory functions and visual perception are discussed. Possible therapeutic for movement disorders and depression are discussed. On the basis of theoretical considerations and current experience rTMS induced epileptogenic effects are discussed and safety recommendations are given.

Brain Mapping↗

PubMed1997

A new variant of progressive encephalomyelitis with rigidity associated with cerebellar ataxia and dementia: correlation of MRI and histopathological changes. A case report.

A 27 year-old patient developed a progressive neurological multisystem disorder. Initial signs were cerebellar ataxia and dementia, followed by rigidity and oculomotor dysfunction. Myoclonus was not present. MRI showed a marked atrophy of the spinal cord, the cerebellum, and mild (sub)cortical atrophy. CSF contained oligoclonal bands, but no anti-glutamic acid dehydrogenase antibodies. He died 33 months after onset of symptoms. Autopsy revealed widespread neuropathological alterations including perivascular lymphocytic cutting, neuronal cell loss, and micro/astrogliosis the distribution of which corresponded to the changes seen in MRI. The diagnosis of progressive encephalomyelitis with rigidity was pathohistologically confirmed. Brain samples were negative for neurotrophic viruses tested by polymerase chain reaction. A new variant of this rare disorder is described initially presenting with ataxia and dementia, but without myoclonus.

Adult↗

PubMed1995

Vasospastic amaurosis fugax in a patient with overlap collagenosis treated with nimodipine.

Vasospasm has been discussed as a less frequent cause of amaurosis fugax. Since its direct demonstration is difficult, its diagnosis is usually based on the exclusion of other causes and/or response to calcium entry blockers. We describe diagnosis and successful treatment of vasospastic amaurosis fugax in a patient with systemic autoimmune disease: A 54 year-old patient with an overlap collagenosis presented with relapsing episodes of transient monocular blindness. Angiography and transcranial Doppler scanning revealed a high-grade stenosis of the left ophthalmic artery. After administration of oral nimodipine the attacks ceased immediately and repeated Doppler examinations confirmed resolution of the stenosis. We infer that vasospasm of inflammatory altered cerebral vessels may contribute to focal neurological deficits in patients with systemic autoimmune disease. Calcium entry blockers should be discussed as a possible treatment in patients with systemic autoimmune disease and evidence of functional disturbances of cerebral blood flow.

Blindness↗