Distinct Mechanism of Audiovisual Integration With Informative and Uninformative Sound in a Visual Detection Task: A DCM Study

Previous studies have shown that task-irrelevant auditory information can provide temporal clues for the detection of visual targets and improve visual perception; such sounds are called informative sounds. The neural mechanism of the integration of informative sound and visual stimulus has been investigated extensively, using behavioral measurement or neuroimaging methods such as functional magnetic resonance imaging (fMRI) and event-related potential (ERP), but the dynamic processes of audiovisual integration cannot be characterized formally in terms of directed neuronal coupling. The present study adopts dynamic causal modeling (DCM) of fMRI data to identify changes in effective connectivity in the hierarchical brain networks that underwrite audiovisual integration and memory. This allows us to characterize context-sensitive changes in neuronal coupling and show how visual processing is contextualized by the processing of informative and uninformative sounds. Our results show that audiovisual integration with informative and uninformative sounds conforms to different optimal models in the two conditions, indicating distinct neural mechanisms of audiovisual integration. The findings also reveal that a sound is uninformative owing to low-level automatic audiovisual integration and informative owing to integration in high-level cognitive processes.

Biological Restraint on the Izhikevich Neuron Model Essential for Seizure Modeling

We propose a simple modification of the Izhikevich neuron model to restrict firing rates of neurons. We demonstrate how this modification affects overall network activity using a simple artificial network. Such restraint on the Izhikevich neuron model would be especially important in larger scale simulations or when frequency dependent short-term plasticity is one of the network components. Although maximum firing rates are most likely exceeded in simulations of seizure like activity or other conditions that promote excessive excitation, we show that restriction of neuronal firing frequencies has impact even on small networks with moderate levels of input.