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Biomedical subjects

I Bodis-Wollner

Publications and source records attributed to I Bodis-Wollner.

At least 19 recordsLinked to original sources
PubMed2006

Role of the calcarine cortex (V1) in perception of visual cues for saccades.

OBJECTIVE: To determine the initial level at which the pathways for cue perception, saccades and antisaccades diverge. METHODS: Two procedures: single pulse transcranial magnetic stimulation (sTMS) over posterior occiput and backward masking were used. A visual cue directed saccades to the left or right, either a pro-saccade (to the side of the cue but beyond it) or an antisaccade, i.e., contraversive saccade. No visual target was presented. RESULTS: Latencies of the two types of saccades did not differ. Focal sTMS applied unilaterally over V1 suppressed both perception of a cue flashed 80-90ms earlier contralaterally (but not ipsilaterally) and the appropriate saccade. Masking at a delay of 100ms abolished the appropriate saccade and cue perception. CONCLUSIONS: V1 is essential for the perception of a flashed cue and for executing appropriate pro- and contraversive saccades. Masking may occur beyond V1, where the pathways for perception and for saccades at least to the next visual processing level start separating. SIGNIFICANCE: VI is needed for rapid, accurate perceptual and motor responses to the crudest (left versus right) cues. It is unlikely that the "where" system can have a major direct input bypassing V1.

Attention↗
PubMed2006

Getting around and communicating with the environment: visual cognition and language in Parkinson's disease.

Vision in PD. In PD an impairment of dopaminergic neurons of the preganglionic retina and a defect of the retinal nerve fibers (axons of the retinal ganglion cells) has been demonstrated and a correlation of loss of spatial contrast sensitivity, with the progression of motor impairment in PD has been described. These low level visual deficits contribute but do not directly explain behavioural visual deficits in PD involving spatial cognition, internal representation, space navigation and visual categorization. Language deficits in non-demented PD patients can include impairments in comprehension, verbal fluency, and naming. Comprehension deficits become evident when patients are required to process sentences with non-canonical, irregular grammatical structures. Semantic memory deficits may result in the impairments in category fluency and confrontational naming. Selective language deficits may be due to impaired dynamics of the "phonological loop" connecting the pre-frontal cortex and the basal ganglia. A more encompassing linguistic and functional model of PD specific language impairments would be useful for evaluating language deficits in the context of motor dysfunction.

Animals↗
PubMed2004

Nicotinic receptors and cognition in Parkinson's Disease: the importance of neuronal synchrony.

Parkinson's Disease (PD) is associated with cognitive deficits. The earliest impairment is evident for executive abilities, visuospatial orientation and memory. Dopamine deficiency is unlikely to be singly responsible for all cognitive changes in PD. Acetyl-choline has an essential role in cognition, thus cholinergic transmission may have an important role in non-dopaminergic cognitive changes. If so, some cognitive defects could possibly be treated with choline-esterase inhibitors. A concern is the potential negative motor effect of cholinergic medication in PD. Surprisingly, these are reported only in a few patients studied. Establishing the relationship between select cognitive deficits and nicotinic neurotransmission may lay the foundation for rational pharmacotherapy of cognitive dysfunction in PD. We summarize anatomical, physiological and pharmacological aspects of nicotinic receptor function. The focus is on those nicotine receptor dependent cognitive dysfunctions which are likely to contribute to motor impairment. Lastly, we discuss hypotheses concerning cholinergic involvement in neuronal synchrony and sensorimotor integration in PD.

Cholinergic Agents↗
PubMed2002

The visuo-cognitive and motor effect of amantadine in non-Caucasian patients with Parkinson's disease. A clinical and electrophysiological study.

It has been reported that non-Caucasian populations often suffer from an atypical type of Parkinson's disease (PD) characterized by poor levodopa response, early cognitive impairment and autonomic dysfunction. We tested the effect of a well known antiparkinsonian compound, amantadine, in 23 Afro-American patients with PD in a time-limited (six months), open-label, clinical and electrophysiological (simultaneously recorded primary and cognitive visual evoked potentials) trial. Patients were given amantadine either as monotherapy (first group) or added to levodopa treatment (second group). Amantadine produced a significant (p < 0.05) shortening of the latency of the event related potential (P300) obtained in a visual discrimination paradigm, while the timing of primary visual evoked potentials was little or not at all affected. Amantadine also showed significant beneficial effects (p < 0.01) on the motor score of both groups as assessed by the Rated Parkinson's Disease Neurological Exam, including items related to autonomic dysfunction. These findings suggest that amantadine alone and as adjuvant to levodopa can significantly improve both the speed of visual cognitive processing and the clinical score in non caucasian patients with PD. For these populations amantadine can be thus considered a helpful therapeutical option.

Black or African American↗
PubMed2001

The paracentral visual field in multiple sclerosis: evidence for a deficit in interneuronal spatial summation?

A visual complaint such as blurred or "washed-out vision" can be one of the early signs of multiple sclerosis (MS). Although visual deficits are commonly attributed to optic nerve demyelination even with preserved visual acuity, the results of a considerable number of visual studies are inconsistent with this interpretation [Camisa, Mylin, & Bodis-Wollner, Annals of Neurology 10 (1981) 532-539; Regan & Neima, British Journal of Ophthalmology 68 (1984) 310-315]. However, a retinal axonal (nerve fiber layer) defect can be detected in some eyes, this is not the rule. Routine visual field (VF) tests, with a low sampling rate may also be non-informative in MS and optic neuritis, possibly because the VF abnormalities may be small and spotty or they can be found between tested points. The present study combined the advantages of VF and contrast sensitivity (CS) testing by applying contrast perimetry (CP), to the central 16 degrees of the VF. Four paracentral VF quadrants were tested in clinically affected and unaffected eyes of 31 MS patients and 26 controls. The stimuli were vertical Gaussian apertured sinusoidal gratings (Gabors) of 1 cpd. CS was obtained as a function of the diameter of the Gábor ranging from 1 to 7.4 degrees. The CP data of controls and definite and probable MS groups were significantly different for each pattern size, but the largest difference was found at diameters 2.5-3.7 degrees. Our study adds to previous evidence showing that optic nerve pathology does not explain "subclinical" and manifest visual dysfunction in MS. Given previous studies revealing orientation dependent monocular visual deficits and our study results, parsimony suggests that MS affects a network relying on myelinated lateral axonal branches of the visual cortex, binding monocular columns of neurons with like-with-like specificity.

Adult↗
PubMed2001

Parkinson's disease changes the balance of onset and offset visual responses: an evoked potential study.

OBJECTIVES: We investigated whether the transient pattern onset and offset visual evoked potential (VEP) can distinguish between patients with Parkinson's disease (PD) and normal subjects. METHODS: Two horizontal sinusoidal gratings differing in spatial frequency, i.e. 1 and 4 cycles per degree, were presented to 17 patients with PD and 16 age-matched control subjects. We analyzed the responses in the time-domain and measured the latencies and amplitudes of N1 and P1 to the onset and the offset of the stimulus; we also derived the measures of offset N1 and P1 amplitude responses 'normalized' to onset N1 and P1 amplitude values, respectively (amplitude ratios). RESULTS: Absolute and normalized offset P1 amplitude is a distinguishing feature of PD patients from controls. Offset P1 amplitude was significantly larger in PD patients than in controls, particularly to the lower spatial frequency stimulus (P<0.01 for absolute and P<0.001 for normalized values, respectively). CONCLUSIONS: We conclude that the pattern onset/offset VEP amplitude provides a simple measure to evaluate visual processing deficits in PD and could contribute to an understanding of the pathophysiology of these changes.

Adult↗
PubMed2001

Retinocortical gain in the foveal pathway: the effect of spatial frequency and stimulus size.

The amplitude and the phase of the simultaneously recorded steady-state pattern electroretinogram (PERG) and visual evoked potential (VEP) were evaluated in humans as a function of the vertical diameter (D) of unidimensional Gabor stimuli. In the other dimension, parallel to the horizontal gratings, the patterns all had constant diameter (see Methods and Materials). Spatial frequencies (SFs) of 1 cycle per degree (cpd) and 5.3 cpd were counterphase modulated at a rate of 6.8 Hz. After off-line artifact rejection, the response was subject to Fast Fourier Transformation (FFT). Amplitude and phase of the first and second harmonics of both ERG and VEP were displayed for each SF and stimulus diameter. Both ERG and VEP amplitude were found to increase as a function of D. Using trend analysis we found that ERG amplitude increased linearly as a function of D. VEP amplitude was found to be both linear and cubic, as a function of D. We calculated the ratio of VEP amplitude and ERG amplitude at each D and termed it retinocortical gain (G). G normalized to stimulus area was high for small D and decreased with D independently of SF. Unity gain occurred at stimulus sizes of 6 degrees to 7 degrees. ERG phase was found to be more negative at 5.3 cpd than at 1 cpd. Although no significant difference was found between VEP phases at the two SFs tested, neither ERG nor VEP phase changed as a function of D. The results suggest that retinocortical gain is highest for the foveally centered low spatial frequency small patch Gabors. The results provide support for the notion of the "foveal window" in human vision.

Adult↗
PubMed2001

Wavelet transform of the EEG reveals differences in low and high gamma responses to elementary visual stimuli.

Multiunit electrophysiological studies indicate that oscillatory activity is common in the awake mammalian central nervous system. Synchronous 20-80 Hz oscillations, so called gamma rhythms, have been proposed as a possible fundamental physiological mechanism of binding neuronal activity underlying object recognition. The purpose of this study was to determine whether or not gamma band oscillatory activity in the human brain is modulated by attributes of elementary visual stimulation. The experiment was performed on 7 normal subjects. Sinusoidal gratings were presented over a range of spatial frequencies. Evoked potentials were recorded over 5 surface electrodes placed in a horizontal occipital chain across the back of the head. Discrete wavelet transform was performed on the first 200 msec following stimulus onset on the average data of 256 sweeps. Power was analyzed with ANOVA across conditions. In our previous studies we have separated a "low" (14-28 Hz) and "high" (28-55 Hz) gamma band. The current results indicate that both gamma bands to full-field stimulation have the highest power at the midline (inion) electrode to a spatial frequency of 5.5 cpd, which is the peak spatial frequency from foveal psychophysical data. However, the spatial frequency bandwidth is considerably narrower in the HG than in the LG band. Occipital spatial frequency tuning of the massed high gamma response is narrower than the tuning of individual cortical neurons. The bandwidth difference between low and high gamma band suggests that different frequency gamma range oscillations may represent not only different functional properties of visual processing, but may also reflect underlying differences in excitatory and postsynaptic inhibitory circuits shaping the contrast sensitivity of the human observer. Our study emphasizes the importance of elementary visual filter properties for gamma responses and the need to subdivide gamma frequency ranges according to functional properties.

Adolescent↗
PubMed2000

Functional properties of sub-bands of oscillatory brain waves to pattern visual stimulation in man.

The scalp recorded transient visual evoked potential (VEP) represents the massed activity of a large number of neurons of the human visual cortex. Animal studies show that intracerebrally-recorded high frequency electrical activity represents binding between neurons participating in a cooperative response. We evaluated the relationship between scalp recorded high frequency activity and transient VEPs elicited by a repetitive (grating) pattern. Stimuli were 1 and 4 cycles/degree sinusoidal gratings, presented in an on/off mode. Following conventional averaging, the discrete wavelet transform (DWT) was applied. Multi-resolution decomposition was used to divide the responses into 6 orthogonal frequency bands. The results show that high frequency oscillatory activity in the beta and gamma frequency range is closely related in time to the N70 peak of the simultaneous VEP. Power in both bands is modulated by spatial frequency. Beta range response to hemifield stimulation recorded over a chain of electrodes over the occipital area lateralizes in the same manner as N70, while gamma range activity is insensitive to lateralization and is more closely linked to foveal stimulation. This dissociation between beta and gamma range activity suggests that different bands of high frequency oscillatory activity in humans, linked to visual stimulation, may represent different aspects of visual processing.

Adolescent↗
PubMed2000

Psychophysical examination of paracentral defects in glaucoma.

More than 50% of ganglion cells may be damaged before visual field loss is measurable by conventional methods in primary open angle glaucoma. There is general agreement on the need to improve early diagnosis of visual field loss in primary open angle glaucoma. In this article, new techniques that enlist measurement of paracentral regions are discussed, and the ability of each method to detect visual field loss prior to perimetric loss is described.

Diagnosis, Differential↗
PubMed1999

Cortical activation patterns during voluntary blinks and voluntary saccades.

OBJECTIVE: To investigate the activation of frontal, parietal, and occipital areas in normal volunteers during voluntary blinks and during voluntary saccades using functional MRI (fMRI). BACKGROUND: A previous fMRI study revealed the activation of the precentral and posterior middle frontal gyrus ("frontal eye field" [FEF]), the medial part of the superior frontal gyrus ("supplementary eye field" [SEF]), and the visual cortex. The parietal cortex was not included in this study. Frontal and occipital cortical areas involved in voluntary blinking have not been shown previously using fMRI. METHODS: A 1.5-T standard clinical scanner was used for both anatomic and functional studies in 12 observers. To conduct data analyses the authors used voxel-by-voxel cross-correlation. RESULTS: Voluntary blinks led to the activation (p < 0.05) of the FEF, the SEF, the posterior parietal cortex ("parietal eye field" [PEF]), and the visual cortex. Voluntary blinking produced activity in the same cerebral structures as voluntary saccades. However, the number of activated voxels was smaller during voluntary blinking than during voluntary saccades in the visual cortex and in the FEF (p < 0.01). In contrast, the extent of activation was significantly higher (p < 0.003) in the SEF and in the PEF during voluntary blinking. CONCLUSIONS: Voluntary blinks and saccades are associated with similar loci of activation patterns; however, the quantitative distribution of activation suggests that the middle part of the frontal gyrus and posterior parietal cortex are of special significance for voluntary blinks. The results argue for the importance of considering quantitative distributional properties of parallel cortical activities associated with saccades and blinks.

Adult↗
PubMed1999

A mixed D1 and D2 antagonist does not replay pattern electroretinogram alterations observed with a selective D2 antagonist in normal humans: relationship with Parkinson's disease pattern electroretinogram alterations.

The human retina produces a tuned response to stimuli of increasing spatial frequency reversed at a steady state. The peak amplitude response, at medium spatial frequencies, is decreased in Parkinson's disease and in normal subjects (n = 18) treated with a D2 dopaminergic antagonist (l-sulpiride). Here, we report that a mixed D1-D2 receptor antagonist (haloperidol) in normal subjects (n = 18) does not produce an amplitude decrease of medium spatial frequencies (SFs) responses but it decreases low-frequency response. It could argued that the increased dopamine release produced by the presynaptic D2 antagonistic action of haloperidol is subsequently counteracted at postsynaptic level by its D1 antagonistic effect, producing a net counterbalance at medium SFs. These data suggest that the two dopamine receptors may play different roles in the retinal function and in the origin of visual alterations in Parkinson's disease.

Adult↗
PubMed1999

L-alpha-glycerylphosphorylcholine enhances the amplitude of the pattern electroretinogram in rhesus monkeys. A pilot study.

The effects of L-alpha-glyceryl-phosphorylcholine (LGPC), a putative acetylcholine precursor, were studied on the pattern electroretinogram (PERG) in two rhesus monkeys. In the time interval 10-30 min after LGPC administration (85 mg/kg i.m.), the amplitude of the PERG increased significantly. In both monkeys the amplitude enhancement was more pronounced for low spatial frequency stimuli (1 cycle/degree) than for medium spatial frequency gratings (5 cycles/degree). This result suggests that besides the general facilitatory properties, LGPC may have specific spatial frequency tuning effects at the level of retinal information processing.

Analysis of Variance↗
PubMed1998

D1 agonist CY208-243 attenuates the pattern electroretinogram to low spatial frequency stimuli in the monkey.

We investigated whether or not the D1 agonist, CY 208-243, affects the spatial tuning function of pattern electroretinogram (PERG). Two lightly anaesthetised monkeys were studied before and after CY 208-243 or placebo administration. The results show that the PERG response to 0.5 cycles/degree (c/d; coarse), but not to 2.3 c/d (medium) spatial frequency stimuli disappears following systemic administration of this drug. Since previous results show that D2 blockers attenuate the PERG only above 2.3 c/d, foremost the peak of the normal spatial frequency response function, the current results suggest that dopamine itself, via D1 receptors, may be responsible for the low spatial frequency decline of normal spatial PERG tuning function. We infer that the synergistic activation of D1 and D2 receptors is needed to shape the spatially tuned primate ERG.

Animals↗
PubMed1998

The push-pull action of dopamine on spatial tuning of the monkey retina: the effects of dopaminergic deficiency and selective D1 and D2 receptor ligands on the pattern electroretinogram.

Retinal dopamine depletion in monkeys using either systemic MPTP or 6-OHDA results in attenuated electroretinographic (ERG) responses to peak spatial frequency stimuli. Diverse dopamine receptors have been identified in the primate retina. ERG studies performed using Haloperidol (a mixed antagonist), L-Sulpiride (D2 antagonist) and CY 208-243 (a D1 agonist) cause spatial frequency dependent diverse effects. 'Tuning' of the normal spatial contrast response PERG, was quantified by dividing the amplitude of the response at the peak spatial frequency with the amplitude to the low spatial frequency response yielding a number greater than one. Tuning for the pharmacological experiments was defined by dividing the actual amplitude obtained at the normal peak response with the actual amplitude at the low spatial frequency response. The PERG spatial contrast response function is discussed as the envelope output of retinal ganglion cells or the average or 'equivalent' retinal ganglion cell. However, we postulate the existence of two dopamine sensitive pathways with different weights for two classes of ganglion cells. It is inferred that D1 receptors are primarily affecting the 'surround' organization of ganglion cells with large centers, while D2 post-synaptic receptors contribute to 'center' response amplification of ganglion cells with smaller centers. These inferences are consistent with some lower vertebrate data. It is also inferred that low affinity D2 autoreceptors may be involved in the D1 'surround' pathway. An understanding of the logic performed by retinal D1 and D2 receptors may be useful to discern the functional role of diverse dopamine receptors in DA circuits elsewhere in the CNS.

Animals↗
PubMed1998

Visuo-cognitive dysfunctions in Parkinson's disease.

Loss of will, decreased activity, and poverty of behavior are among the common symptoms observed in Parkinson's disease (PD). In line with these clinical observations, PD patients display prominent deficit in neuropsychological tests, requiring self-generated and effort-demanding operations. However, recent evidence suggests that this impairment is not generalized: visuo-spatial working memory and attentional set-shifting seem to be selectively impaired in the early stages of the disease. Electrophysiological studies also demonstrate the dysfunction of higher-level visual information processing. In this article, we discuss some current results to show the connection between clinical symptoms and neuropsychological deficits. We also consider dysfunction in underlying neural mechanisms, with particular emphasis on the dysregulation of fronto-striatal circuits. However, it is conceivable that visuo-cognitive impairment in PD reflects dysfunction of neural assemblies, involving basal ganglia, dorsal visual stream, and frontal-prefrontal circuits.

Attention↗
PubMed1997

Dopamine D2 receptor blockade alters the primary and cognitive components of visual evoked potentials in the monkey, Macaca fascicularis.

The effects of sulpiride, a dopamine D2 receptor antagonist, were studied on visual event-related potentials in a monkey performing in a visual oddball task in order to investigate receptor specific mechanisms in visuo-cognitive processes. Following the injection of 0.35 mg/kg sulpiride i.m., the amplitude and latency of the primary (P100) and cognitive (P300) components did not change significantly. When 1.05 mg/kg sulpiride was administered, the latency of the primary and cognitive components increased. The amplitude of the P100 component decreased, while that of the P300 component increased. These data suggest that D2 receptors play an important role in visuo-cognitive processes in both physiological and pathological conditions such as Parkinson's disease and schizophrenia.

Animals↗