Parvocellular and magnocellular visual processing in spinocerebellar degeneration and Parkinson's disease: an event-related potential study

Visual mismatch negativity in the dorsal stream is independent of concurrent visual task difficulty

The manipulation of attention can produce mismatch negativity-like components that are not necessarily connected to the unintentional sensory registration of the violation of probability-based regularity. For clinical purposes, attentional bias should be quantified because it can vary substantially among subjects and can decrease the specificity of the examination. This experiment targets the role of attention in the generation of visual mismatch negativity (vMMN). The visual regularity was generated by a sequence of two radial motions while subjects focused on visual tasks in the central part of the display. Attentional load was systematically varied and had three levels, no-load, easy, and difficult. Rare, deviant, and frequent standard motions were presented with a 10/60 ratio in oddball sequences. Data from 12 subjects was recorded from 64 channels and processed. vMMN was identified within the interval of 142-198 ms. The mean amplitude was evaluated during the aforementioned interval in the parietal and fronto-central regions. A general linear model for repeated measures was applied to the mean amplitude with a three-factor design and showed a significant difference [F (1, 11) = 17.40, p = 0.002] between standard and deviant stimuli and between regions [F (1, 11) = 8.40, p = 0.01]; however, no significant effect of the task [F (2, 22) = 1.26, p = 0.30] was observed. The unintentional detection of irregularity during the processing of the visual motion was independent of the attentional load associated with handling the central visual task. The experiment did not demonstrate an effect of attentional load manipulation on mismatch negativity (MMN) induced by the motion-sequence, which supports the clinical utility of this examination. However, used stimulation paradigm should be further optimized to generate mismatch negativity that is stable enough to be usable not only for group comparisons but also for a single subject assessment.

The temporal dynamics of coherent motion processing in autism spectrum disorder: evidence for a deficit in the dorsal pathway

Individuals with autism spectrum disorder (ASD) show impairments in processing coherent motion which have been proposed to be linked to a general deficit in the dorsal visual pathway. However, few studies have investigated the neural mechanisms underlying coherent motion processing in ASD. Thus, the aim of this study was to further test the hypothesis of a dorsal pathway deficit in ASD using visual evoked potentials (VEPs). 16 children and adolescents with ASD and 12 typically developing controls were examined with VEPs elicited by a random dot kinematogram. After an initial experimental sequence, where subjects were presented randomly moving dots, a fraction of the dots moved coherently (dependent on the level of coherence, 20%, 40%, or 60% of the dots) to the left or right side. Subjects were asked to detect the direction of coherent motion via button press. On the behavioural level, no significant group differences emerged. On the neural level, coherently moving dots elicited a N200 followed by a late positive potential (P400). ASD subjects exhibited a reduced N200 amplitude compared to controls. Moreover, in the ASD group, a trend for a negative relationship between N200 amplitude and a measure of autistic pathology was revealed. The present study provides strong support of a dorsal stream deficiency in the disorder and renders alternative explanations for impaired coherent motion processing in ASD less likely. Together with findings from related research fields, our data indicate that deviances in the N200 during coherent motion perception might be fundamental to ASD.

Psychometrically matched tasks evaluating differential fMRI activation during form and motion processing

OBJECTIVE

Deficits in visual perception and working memory are commonly observed in neuropsychiatric disorders and have been investigated using functional MRI (fMRI). However, interpretation of differences in brain activation may be confounded with differences in task performance between groups. Differences in task difficulty across conditions may also pose interpretative issues in studies of visual processing in healthy subjects.

METHOD

To address these concerns, the present study characterized brain activation in tasks that were psychometrically matched for difficulty; fMRI was used to assess brain activation in 10 healthy subjects during discrimination and working memory judgments for static and moving stimuli. For all task conditions, performance accuracy was matched at 70.7%.

RESULTS

Areas associated with V2 and V5 in the dorsal stream were activated during motion processing tasks and V4 in the ventral stream were activated during form processing tasks. Frontoparietal areas associated with working memory were also statistically significant during the working memory tasks.

CONCLUSIONS

Application of psychophysical methods to equate task demands provides a practical method to equate performance levels across conditions in fMRI studies and to compare healthy and cognitively impaired groups at comparable levels of effort. These psychometrically matched tasks can be applied to patients with a variety of cognitive disorders to investigate dysfunction of multiple a priori defined brain regions. Measuring the changes in typical activation patterns in patients with these diseases can be useful for monitoring disease progression, evaluating new drug treatments, and possibly for developing methods for early diagnosis.

Foveal evoked magneto-encephalography features related to the parvocellular pathway

The aim of this study was to use non-invasive magneto-encephalographic techniques, together with visual stimulus paradigms that can psychophysically separate the M- and P-pathways, to examine the physiological relations of the pathways at the fovea with (1) the magneto-encephalography components M70 and M100 (in latency and amplitude), and (2) the cortical oscillatory activities (alpha, beta, and gamma), respectively. The checkerboard stimuli accompanied with different spatial frequencies (SFs) (0.5 or 4 cycles per degree) were presented (within 2 degrees of the retinal center) to six healthy subjects by using steady-pedestal and pulse paradigms, which could activate distinct populations of M- and P-neurons. SF analyzed brain responses in each paradigm. The results show a consistent trend in M70 and M100 with increased latencies and amplitudes in response to the high SF. Mean while, the beta to gamma activities are apparently enhanced by the stimulus of high SF, especially under pulse paradigm (p = 0.03). In this study, we suggest that M70 can be a good clue to characterize the P-pathway. Moreover, in the frequency analysis, the beta oscillations may serve for more detailed visual information, while the gamma oscillations seem to reflect the signal processing in the P-pathway and with sensitivity to the fovea.

A primer on motion visual evoked potentials

Motion visual evoked potentials (motion VEPs) have been used since the late 1960s to investigate the properties of human visual motion processing, and continue to be a popular tool with a possible future in clinical diagnosis. This review first provides a synopsis of the characteristics of motion VEPs and then summarizes important methodological aspects. A subsequent overview illustrates how motion VEPs have been applied to study basic functions of human motion processing and shows perspectives for their use as a diagnostic tool.

Non-invasive evaluation of face and motion perception in humans

The neural mechanisms for the perception of face and motion were studied using psychophysical threshold measurements, event-related potentials (ERPs), and functional magnetic resonance imaging (fMRI). A face-specific ERP component, N170, was recorded over the posterior temporal cortex. Removal of the high-spatial-frequency components of the face altered the perception of familiar faces significantly, and familiarity can facilitate the cortico-cortical processing of facial perceptions. Similarly, the high-spatial-frequency components of the face seemed to be crucial for the recognition of facial expressions. Aging and visuospatial impairments affected motion perception significantly. Two distinct components of motion ERPs, N170 and P200, were recorded over the parietal region. The former was related to horizontal motion perception while the latter reflected the perception of radial optic flow motion. The results of fMRI showed that horizontal movements of objects and radial optic flow motion were perceived differently in the V5/MT and superior parietal lobe. We conclude that an integrated approach can provide useful information on spatial and temporal processing of face and motion non-invasively.

Effect of stimulus localisation on motion-onset VEP

Reliable motion-onset visual evoked potentials (result of the dorsal stream activation) were recorded to motion stimuli with the temporal frequency of five cycles per seconds in 20 different locations with eccentricity up to 42 degrees to periphery of the visual field. Amplitudes and latencies of the positive-negative-positive (P1-N1-P2; 84-144-208 ms) complex were evaluated in occipital (OZ and two derivations 5 cm to the left and right from OZ) and central region (CZ) in 10 subjects. We observed: (1) Shortening of the N1 latency toward periphery of the visual field. (2) The N1 amplitude maximum and latency minimum moved from occipital into central region (CZ derivation) as stimulus moved from centre toward periphery of visual field. (3) The P1 and N1 peaks displayed significantly greater amplitudes and shorter latencies when the lower part of the visual field was stimulated. (4) The N1 peak changed lateralisation of its maximum amplitude in dependence on the eccentricity. Up to 17 degrees, it corresponds to striate projection of the "optic radiation" whilst more in periphery, there was paradoxical lateralisation of higher amplitude and shorter latency. The retinotopic dependence shows that the motion response includes position information and that the motion-onset VEPs are not generated solely in the higher extrastriate areas (MT or MST).

Electrophysiological correlates of associative visual agnosia lesioned in the ventral pathway

Visual agnosia has been well studied by anatomical, neuropsychological and neuroimaging studies. However, functional changes in the brain have been rarely assessed by electrophysiological methods. We carried out electrophysiological examinations on a 23-year-old man with associative visual agnosia, prosopagnosia and cerebral achromatopsia to evaluate the higher brain dysfunctions of visual recognition. Electrophysiological methods consisted of achromatic, chromatic and category-specific visual evoked potentials (CS-VEPs), and event-related potentials (ERPs) with color and motion discrimination tasks. Brain magnetic resonance imaging revealed large white matter lesions in the bilateral temporo-occipital lobes involving the lingual and fusiform gyri (V4) and inferior longitudinal fasciculi due to multiple sclerosis. Examinations including CS-VEPs demonstrated dysfunctions of face and object perception while sparing semantic word perception after primary visual cortex (V1) in the ventral pathway. ERPs showed abnormal color perception in the ventral pathway with normal motion perception in the dorsal pathway. These electrophysiological findings were consistent with lesions in the ventral pathway that were detected by clinical and neuroimaging findings. Therefore, CS-VEPs and ERPs with color and motion discrimination tasks are useful methods for assessing the functional changes of visual recognition such as visual agnosia.

Neuro-ophthalmology of movement disorders

Movement disorders are a diverse group of neurologic disorders that share in common the frequent development of clinical abnormalities in ocular motility or visual perception. This article reviews the recent literature pertaining to the neuro-ophthalmologic advances in the basal ganglia disorders (Parkinson disease, progressive supranuclear palsy, corticobasal degeneration, multiple system atrophy, and Huntington disease), the spinocerebellar ataxias and episodic ataxias, amyotrophic lateral sclerosis, benign essential blepharospasm, hemifacial spasm, and Tourette syndrome.