PubMed · 16614835
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Talis Bachmann, Mark Elliott, Michael Herzog, Dirk Vorberg. 2007. Visual perception in a snapshot.. https://doi.org/10.1007/s00426-006-0050-x
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The ultimate goal of brain connectivity studies is to propose, test, modify, and compare certain directional brain pathways. Path analysis or structural equation modeling (SEM) is an ideal statistical method for such studies. In this work, we propose a two-stage unified SEM plus GLM (General Linear Model) approach for the analysis of multisubject, multivariate functional magnetic resonance imaging (fMRI) time series data with subject-level covariates. In Stage 1, we analyze the fMRI multivariate time series for each subject individually via a unified SEM model by combining longitudinal pathways represented by a multivariate autoregressive (MAR) model, and contemporaneous pathways represented by a conventional SEM. In Stage 2, the resulting subject-level path coefficients are merged with subject-level covariates such as gender, age, IQ, etc., to examine the impact of these covariates on effective connectivity via a GLM. Our approach is exemplified via the analysis of an fMRI visual attention experiment. Furthermore, the significant path network from the unified SEM analysis is compared to that from a conventional SEM analysis without incorporating the longitudinal information as well as that from a Dynamic Causal Modeling (DCM) approach.
BACKGROUND: Impulsivity, a core feature of bipolar disorder (BD), is a multifaceted concept encompassing failure of response inhibition and poor decision-making. Abnormalities in these two cognitive domains have been reported in BD patients but their relationship with impulsivity has not been explored. METHODS: Twenty-five remitted patients with BD completed the Barratt Impulsiveness Scale (BIS) and performed the Hayling Sentence Completion Task (HSCT) and a computerized version of the Iowa Gambling task. The HSCT total errors scaled score was used as a measure of response inhibition while the gabling task score, which reflects participants' ability to make advantageous choices, was used a measure of decision making. RESULTS: Higher scores on the BIS attentional and non-planning subscales were respectively associated with more errors in the HSCT and less advantageous choices in the gambling task. LIMITATIONS: All patients were medicated. Healthy participants were not included. CONCLUSIONS: Viewed in the context of recent relevant studies our findings suggest that impulsivity, response inhibition and decision-making in BD may represent behavioural manifestations of the same underlying biological mechanism possibly linked to ventral prefrontal cortical function.
Sensory cueing is used for a long time to improve gait in patients with Parkinson's disease. This has been established for visual cues such as stripes on floor and for rhythmic auditory cues. Concerning visual cueing two main mechanisms of action have been suggested and may be suitable depending on the instruction given to the patients. Stripes placed on the walking surface may draw attention to the stepping process if patients are talked to put their feet on the stripes. In another paradigm, the stripes on floor are just used to enhance the optical flow and the motion of the stripes is essential to improve gait. These findings are not found in normal controls suggesting that patients with Parkinson's disease are more dependent on dynamic visual cues for gait control than controls. Several common characteristics exist between attention and sensory contribution in gait control. First, their potential beneficial effect may be contre-balanced by a negative influence: visual information may be helpful for gait in patients or may disrupt locomotion and induce freezing (for example passing a door). Attention focused on gait allows a partial correction of the troubles by intentional modulation of the stride length but a dual task flowing attention away produces deterioration. Another point is that both strategies are probably used by the central nervous system to compensate deficits: visual dependence to compensate an impaired kinesthetic feed-back and attentional processing to alleviate automaticity in locomotion and so, to by-pass the deficit of internal cueing.