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Paired associates learning is impaired in both schizophrenia and amnestic mild cognitive impairment (aMCI), which may reflect hippocampal pathology. In addition, schizophrenia is characterized by the dysfunction of the retino-geniculo-striatal magnocellular (M) visual pathway. The purpose of this study was to investigate the interaction between visual perceptual and memory dysfunctions. We administered a modified version of the CANTAB paired associates learning task to patients with schizophrenia (n = 20), aMCI (n = 20), and two groups of matched healthy controls (n = 20 for each patient group). The stimuli in the paired associates learning task biased information processing toward the M pathways (low contrast, low spatial frequency) and parvocellular (P) pathways (high contrast, high spatial frequency). Results revealed that patients with schizophrenia exhibited a more pronounced learning deficit for M-biased relative to P-biased stimuli. In aMCI, there were similar memory deficits for both types of stimuli. Orientation discrimination for M- and P-biased stimuli was intact in both groups of patients. The number of errors in the M-biased memory condition significantly and inversely correlated with the volume of the right hippocampus in schizophrenia. These results suggest an interaction between M-biased perceptual processing and short-term relational memory in schizophrenia, which may be associated with the structural alteration of the right hippocampus. (Contains 3 tables and 3 figures.)

Previous studies reported impaired visual information processing in patients with fragile x syndrome and in premutation carriers. In this study, we assessed the perception of biological motion (a walking point-light character) and mechanical motion (a rotating shape) in 25 female fragile x premutation carriers and in 20 healthy non-carrier controls. Stimuli were moving stimulus dots embedded among a cloud of noise dots. Sensitivity (d) for motion detection was determined. Emotional symptoms were assessed by Hamilton's depression and anxiety rating scales. Results revealed that the premutation carriers displayed lower sensitivities for biological and mechanical motion relative to the non-carriers. This deficit was more pronounced in the case of biological stimuli. The premutation carriers displayed higher depression and anxiety scores relative to the non-carriers. Higher depression, but not anxiety, scores were associated with decreased sensitivity for biological, but not mechanical, motion in the carrier group. These results suggest that motion perception deficits are detectable in fragile x premutation carriers, and that the impairment of biological motion perception is associated with depressive symptoms. (Contains 4 figures and 2 tables.)

Previous studies indicated impaired magnocellular (M) and relatively spared parvocellular (P) visual pathway functioning in patients with fragile X syndrome. In this study, we assessed M and P pathways in 22 female fragile X premutation carriers with normal intelligence and in 20 healthy non-carrier controls. Testing procedure included visual contrast sensitivity and vernier threshold measurements. Results revealed that carriers were selectively impaired on tests of M pathways (low spatial/high temporal frequency contrast sensitivity and frequency-doubling vernier), whereas they showed intact performance on P pathway tests. These results suggest that the deficit of the M pathway is an endophenotype of fragile X syndrome. (Contains 3 figures.)

Schizophrenia is characterized by impaired visual contrast sensitivity and anomalous perceptual experiences. The aim of this study was to investigate these phenomena in unmedicated patients with first-episode schizophrenia. Visual contrast sensitivity was measured with pulsed-pedestal and steady-pedestal tests, which bias information processing toward the parvocellular and magnocellular pathways, respectively. Anomalous perceptual experiences were investigated with the Structured Interview for Assessing Perceptual Anomalies (SIAPA). Results revealed that patients with schizophrenia (n = 20) exhibited increased contrast sensitivity values on the magnocellular test relative to the control participants (n = 20). In the parvocellular condition, there was no significant difference between the two groups. The higher magnocellular contrast sensitivity values were associated with increased visual SIAPA scores, especially at the two lowest spatial frequencies (0.25 and 0.5 cycles/degree). These results indicate the heightened sensitivity of magnocellular pathways in unmedicated first-episode schizophrenia, which may contribute to anomalous perceptual experiences and sensory overloading. Keywords: schizophrenia, first episode, contrast sensitivity, magnocellular pathways, vision DOI: 10.1037/a0019610

[alpha]-Synuclein (SNCA) plays an important role in the regulation of dopaminergic neurotransmission and neurodegeneration in Parkinson disease. We investigated reward and punishment learning in asymptomatic carriers of a rare SNCA gene duplication who were healthy siblings of patients with Parkinson disease. Results revealed that healthy SNCA duplication carriers displayed impaired reward and intact punishment learning compared with noncarriers. These results demonstrate that a copy number variation of the SNCA gene is associated with selective impairments on reinforcement learning in asymptomatic carriers without the motor symptoms of Parkinson disease. Parkinson disease | reinforcement learning | dopamine | basal ganglia doi/ 10.1073/pnas.1006068107

B. F. O'Donnell et al. (2002) found impaired discrimination performances at low and medium spatial frequencies in patients with schizophrenia. In this study, the authors replicated this finding in a group of remitted, unmedicated, and highly functioning outpatients with spared IQ and attentional functions. However, the deficit was restricted to low spatial frequencies (0.5 cycles/degree), which suggests that this deficit is a trait marker of schizophrenia. Keywords: schizophrenia, visual perception, spatial frequency, magnocellular pathway

Skottun and Skoyles (2009) recently presented a comment on Vernier acuity and magnocellular dysfunctions in fragile X premutation carriers (Keri & Benedek, 2009). The authors concluded that our finding that the magnocellular deficit, as revealed by luminance-contrast sensitivity measurements, is associated with impaired Vernier acuity for achromatic gratings does not mean that this procedure is suitable for the investigation of the magnocellular pathways, given that deficits outside the magnocellular system also lead to impaired Vernier acuity. However, Skottun and Skoyles (2009) did not consider the dissociation between achromatic and isoluminant color Vernier and the convergence of Vernier and luminance-contrast sensitivity measurements.

Reviewed by Gyorgy Benedek Developmental scientists have always been receptive to dynamic systems because they come face to face with complexity, nonlinearity, and context dependency every day. The works of [...]

Single unit activity (SUA) was extensively studied in the lateral geniculate nucleus (LGN) but less attention was paid to the analysis of the local field potentials (LFP). In the present study, we investigate how and to what extent LFP and SUA correlate with visual stimulus eccentricity. SUAs and LFPs recorded extracellularly from 52 electrode positions were analyzed. Both LFP and SUA recordings contained well defined time-segments, which correlated with stimulus eccentricity. The spectral analysis of the LFPs indicated that in addition to the phasic, short latency activity of the 20 Hz frequency band, a tonic, 2-10 Hz, elongated component was also present. The time-domain analysis of the phasic and tonic LFP segments revealed a non-linear decrease of the mean LFP amplitude. The frequency-domain investigation made it obvious that the low and high frequency components exhibit a spatially localized increase of the response, in contrast to the time-domain curve. Our results confirm that the local field potentials as a measure of the mesoscopic level neuronal activity provide additional information concerning the activity of neuronal populations, thus enhancing our present knowledge about the functional circuitry as the foundation of various neuronal processes.