Andrés Posada

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Time perception has long been known to be impaired in schizophrenia. Moreover, recent neuropsychological theories have postulated abnormalities of cognitive motor control in schizophrenia. However, the intersection of these two topics has rarely been studied, and it is unclear what role subjects' own actions may play in the construction of subjective time(More)
During the development of the nervous system, a large number of neurons are eliminated through naturally occurring neuronal death. Many morphological and biochemical properties of such dying neurons are reminiscent of apoptosis, a type of death involving the action of genetically-programmed events but also epigenetic phenomena including oxidative stress.(More)
Intentions are central to guiding actions to their completion because they generate expectations which precede the realization of a task. This ability to manage time was investigated by using a cognitive task which involves several highly integrated processes: sequential learning, explicit processing, and working memory. In this task, participants are(More)
Two retrograde signals influence the chick embryo's isthmo-optic nucleus, which projects to the retina: a slow-acting survival signal due to uptake of neurotrophic factors, and a fast-acting death signal initiated by calcium entry into isthmo-optic terminals due to electrical activity. The latter signal also affects dendritic reorganization. Since nitric(More)
Motor imagery provides a direct insight into action representations. The aim of the present study was to investigate the level of impairment of action monitoring in schizophrenia by evaluating the performance of schizophrenic patients on mental rotation tasks. We raised the following questions: (1) Are schizophrenic patients impaired in motor imagery both(More)
About half the neurons in the brain die at the time when their connections are being formed. This neuronal death is regulated by anterograde and retrograde signals that reflect both electrical activity and the uptake of trophic factors. Our recent data on the isthmo-optic projection indicate that there are in fact two different retrograde signals: a(More)
Schizophrenia is characterized by an altered sense of the reality, associated with hallucinations and delusions. Some theories suggest that schizophrenia is related to a deficiency of the system that generates information about the sensory consequences of the actions realized by the subject. This system monitors the reafferent information resulting from an(More)
At the time of synaptogenesis typically 50% of the neurons die. The biological role of this is still unclear, but there is evidence in the visual system that many neurons projecting to topographically inappropriate parts of their target are eliminated to improve the accuracy of the mapping. The signaling that determines neuronal survival involves electrical(More)
Schizophrenia is associated with cognitive deficits and information-processing anomalies. Several studies have shown impairments in frontal lobe functions such as discovering rules, adopting strategies and working memory. We have evaluated the performances of schizophrenic patients on three different tasks of information processing. The first was a simple(More)
Retrograde signals from axon terminal to cell body are known to regulate neuronal survival and differentiation during development. They are generally attributed to the uptake and transport of trophic factors, but there is recent evidence in the isthmo-optic nucleus for a remarkably fast-acting retrograde signal from the contralateral retina that is not(More)