Biomedical subjects

Andreas Stevens

Publications and source records attributed to Andreas Stevens.

3 recordsLinked to original sources

PubMed2005

Neural pattern dynamics in an oscillator model of the thalamo-reticular system.

One of development issues for information processing with synchronous oscillations in the brain is how new information is coded and how a comparison with already existing information is performed. In the present work we study a simple neural network model of the thalamo-reticular system based on the Wilson-Cowan model of neuronal oscillatory behavior. Our results show that both cortical control over the thalamus and external sensory input are essential in coordinating and generating spatio-temporal patterns of synchronous activity. A main finding of the numerical simulations is that the network connectivity and the intrinsic oscillatory properties of the neurons result in distinct collective behaviors within the network. By varying the connectivity schemes comparable with lesionated or damaged brain regions our results are in good agreement with in vivo experimental results. Suppressing the sensory input results in temporal oscillatory activity in the beta and gamma range and a strong spatial dependence of the network activity.

Algorithms↗

PubMed2004

Borderline personality disorder: impaired visual perception and working memory.

The neurobiology of borderline personality disorder (BPD) is still elusive. There are a few studies on neuropsychological performance in BPD, which report a broad spectrum of abnormalities. The present study evaluates perception and working memory as instances of basic cognitive functions. Female subjects diagnosed with DSM-IV borderline personality disorder (n=22) were compared with age- and education-matched controls (n=25). Perception speed was assessed by a backward masking paradigm. Working memory was tested by a series of delayed matching-to-sample paradigms involving varying subsidiary functions like mental rotation, retrieval from memory, ignoring distracters, and cross-modal performance. In backward masking, BPD subjects required significantly longer stimulus onset asynchrony (SOA) than controls to identify the visual target, and there was an additional slowing of the motor response. Working memory accuracy was impaired in BPD subjects, but did not worsen when the cognitive load was increased. With increasing task difficulty, they traded off speed for accuracy similarly as the controls. Impulsivity and dissociation ratings were not correlated with performance. It is concluded that perceptional speed and working memory are impaired in BPD, but that the deficits are not augmented by increasing cognitive load.

Adolescent↗

PubMed2002

Implicit and explicit learning in schizophrenics treated with olanzapine and with classic neuroleptics.

OBJECTIVE: Novel and classic neuroleptics differ in their effects on limbic striatal/nucleus accumbens (NA) and prefrontal cortex (PFC) dopamine turnover, suggesting differential effects on implicit and explicit learning as well as on anhedonia. The present study investigates whether such differences can be demonstrated in a naturalistic sample of schizophrenic patients. METHODS: Twenty-five inpatients diagnosed with DSM-IV schizophrenic psychosis and treated for at least 14 days with the novel neuroleptic olanzapine were compared with 25 schizophrenics taking classic neuroleptics and with 25 healthy controls, matched by age and education level. PFC/NA-dependent implicit learning was assessed by a serial reaction time task (SRTT) and compared with cerebellum-mediated classical eye-blink conditioning and explicit visuospatial memory. Anhedonia was measured with the Snaith-Hamilton-Pleasure Scale (SHAPS). RESULTS: Implicit (SRTT) and psychomotor speed, but not explicit (visuospatial) learning were superior in the olanzapine-treated group as compared to the patients on classic neuroleptics. Compared to healthy controls, olanzapine-treated schizophrenics showed similar implicit learning, but reduced explicit (visuospatial) memory performance. Acquisition of eyeblink conditioning was not different between the three groups. There was no difference with regard to anhedonia and SANS scores between the patients. CONCLUSION: Olanzapine seems to interfere less with unattended learning and motor speed than classical neuroleptics. In daily life, this may translate into better adaptation to a rapidly changing environment. The effects seem specific, as in explicit learning and eyeblink conditioning no difference to classic NL was found.

Adult↗