Orientatie-discriminatie en de visuele cortex : een experimenteel onderzoek bij het konijn

Het zenuwstelsel van mens en dier wordt met verschillende methoden bestudeerd. Di t leidt er vaak toe dat de onderzoeksresultaten met die methoden verkregen, resulteren in het ontstaan van onderling gescheiden subdisciplines. Dit geschiedt ook daar waar in beginsel integratie van vakgebieden technisch wel degelijk mogelijk is. Bij het bestuderen van het visueel systeem vormen de resultaten van electrofysiologisch onderzoek met behulp van micro-electroden een vakgebied op zichzelf. Slechts bij uitzondering wordt getracht verbanden te leggen met resultaten van gedragsexperimenten. In dit proefschrift wordt een poging gedaan om te onderzoeken in hoeverre er verband gelegd kan worden tussen visuele discriminatie experimenten bij het konijn en resultaten van electrofysiologisch onderzoek zoals beschreven in de literatuur. De gedachtengang is eenvoudig. Het konijn is in staat lijnstukken van verschillende helling te onderscheiden. Dit is aangetoond door middel van visuele discriminatie experimenten. Verder is uit dergelijke experimenten gebleken dat na ablatie van de visuele cortex het vermogen om lijnstukken van verschillende orientatie te detecteren - in tegenstelling tot het vermogen om vlakken van verschillende helderheid te discrimineren - verloren is

Evidence for unusual spatial location coding in Williams syndrome: An explanation for the local bias in visuo-spatial construction tasks?

Individuals with Williams syndrome (WS) display poor visuo-spatial cognition relative to verbal abilities. Furthermore, whilst perceptual abilities are delayed, visuo-spatial construction abilities are comparatively even weaker, and are characterised by a local bias. We investigated whether this differentiation in visuo-spatial abilities can be explained by a deficit in coding spatial location in WS. This can be measured by assessing participants? understanding of the spatial relations between objects within a visual scene. Coordinate and categorical spatial relations were investigated independently in four participant groups: 21 individuals with WS; 21 typically developing (TD) children matched for non-verbal ability; 20 typically developing controls of a lower non-verbal ability; and 21 adults. A third task measured understanding of visual colour relations. Results indicated first, that the comprehension of categorical and co-ordinate spatial relations is equally poor in WS. Second, that the comprehension of visual relations is also at an equivalent level to spatial relational understanding in this population. These results can explain the difference in performance on visuo-spatial perception and construction tasks in WS. In addition, both the WS and control groups displayed response biases in the spatial tasks. However, the direction of bias differed across the groups. This finding is explored in relation to current theories of spatial location coding

Saccade Adaptation in Williams-Beuren Syndrome

PURPOSE. To investigate the capacity for rapid saccade adaptation in Williams-Beuren Syndrome (WBS), a genetic neurodevelopmental disorder, in which it has been observed that saccadic accuracy is severely reduced. METHODS. Saccade amplitude modification was elicited by backward steps (30% of target eccentricity) during the primary saccade in a classic saccade-adaptation paradigm. RESULTS. Patients with WBS showed a significant decrease in saccade amplitude. Furthermore, we observed that higher saccade accuracy before adaptation was related to more adaptation. CONCLUSIONS. The increased variability in motor performance does not abolish the ability for saccadic adaptation in subjects with WBS. Our results are congruent with the notion that part of the behavioral deficits observed in WBS may have a cerebellar origin. (Invest Ophthalmol Vis Sci

Comparing Two Diagnostic Laboratory Tests for Williams Syndrome: Fluorescent In Situ

Most people with Williams syndrome (WS) have a heterozygous 1.55 Mb deletion on chromosome 7q11.23. For diagnostic purposes, fluorescence in situ hybridisation (FISH) with commercial FISH probes is commonly used to detect this deletion. We investigated whether multiplex ligation-dependent probe amplification (MLPA) is a reliable alternative for FISH. The MLPA kit (SALSA P029) contains probes for eight genes in the WS critical region: FKBP6, FZD9, TBL2, STX1A, ELN, LIMK1, RFC2, and CYLN2. The experimental FISH assay that was used consists of four probes covering the WS critical region. A total number of 63 patients was tested; in 53 patients, a deletion was detected both with FISH and MLPA(P029), in 10 patients both techniques failed to demonstrate a deletion. In only one patient, a deletion was detected which was not previously detected by two commercial FISH probes. This patient appeared to carry a small, atypical deletion. We conclude that MLPA is a reliable technique to detect WS. Compared with FISH, MLPA is less time consuming and has the possibility to detect also smaller, atypical deletions and duplications in the WS critical region

Contribution of CYLN2 and GTF2IRD1 to neurological and cognitive symptoms in Williams Syndrome

Williams Syndrome (WS, [MIM 194050]) is a disorder caused by a hemizygous deletion of 25-30 genes on chromosome 7q11.23. Several of these genes including those encoding cytoplasmic linker protein-115 (CYLN2) and general transcription factors (GTF2I and GTF2IRD1) are expressed in the brain and may contribute to the distinct neurological and cognitive deficits in WS patients. Recent studies of patients with partial deletions indicate that hemizygosity of GTF2I probably contributes to mental retardation in WS. Here we investigate whether CYLN2 and GTF2IRD1 contribute to the motoric and cognitive deficits in WS. Behavioral assessment of a new patient in which STX1A and LIMK1, but not CYLN2 and GTF2IRD1, are deleted showed that his cognitive and motor coordination functions were significantly better than in typical WS patients. Comparative analyses of gene specific CYLN2 and GTF2IRD1 knockout mice showed that a reduced size of the corpus callosum as well as deficits in motor coordination and hippocampal memory formation may be attributed to a deletion of CYLN2, while increased ventricle volume can be attributed to both CYLN2 and GTF2IRD1. We conclude that the motor and cognitive deficits in Williams Syndrome are caused by a variety of genes and that heterozygous deletion of CYLN2 is one of the major causes responsible for such dysfunctions