Biomedical subjects

Baktash Babadi

Publications and source records attributed to Baktash Babadi.

4 recordsLinked to original sources

PubMed2005

Brain complexity increases in mania.

An important challenge in measuring whole brain activation is to develop a measure that could distinguish between normal and abnormal mood states. The application of chaos theory and non-linear dynamics to problems in biological sciences has resulted in a growing body of advancements and the notion of brain as a complex, non-linear system has attracted physicists, mathematicians, biologists and psychologists alike. To search for a correlation between alterations in chaotic brain states and mood disorders, we compared the fractal dimension of the electroencephalographic (EEG) signal in patients going through a manic episode of bipolar mood disorder (BMD) type I to a control group of healthy adults and showed that the EEG fractal dimension is significantly augmented in our patients. Thus, for the first time, we draw a clear objective distinction between normal and abnormal mood and associated brain states.

Adult↗

PubMed2002

New attractor states for synchronous activity in synfire chains with excitatory and inhibitory coupling.

In a feedforward network of integrate-and-fire neurons, where the firing of each layer is synchronous (synfire chain), the final firing state of the network converges to two attractor states: either a full activation or complete fading of the tailing layers. In this article, we analyze various modes of pattern propagation in a synfire chain with random connection weights and delta-type postsynaptic currents. We predict analytically that when the input is fully synchronized and the network is noise free, varying the characteristics of the weights distribution would result in modes of behavior that are different from those described in the literature. These are convergence to fixed points, limit cycles, multiple periodic, and possibly chaotic dynamics. We checked our analytic results by computer simulation of the network, and showed that the above results can be generalized when the input is asynchronous and neurons are spontaneously active at low rates.

Action Potentials↗

PubMed2002

Munker-White-like illusions without T-junctions.

Some interpretations of the Munker-White illusion were evaluated by designing new versions of this illusion devoid of T-junctions (Munker-White-like images). The magnitudes of both Munker-White and Munker-White-like illusions were then quantified by using a brightness-matching technique. The results showed the effect to persist in all proposed versions. Since the illusion still remains despite the absence of explicit T-junctions and any explanation considering transparency, mechanisms other than those proposed by these interpretations must be responsible.

Contrast Sensitivity↗

PubMedDate not supplied

Bursting as an effective relay mode in a minimal thalamic model.

In recent years, accumulating evidence indicates that thalamic bursts are present during wakefulness and participate in information transmission as an effective relay mode with distinctive properties from the tonic activity. Thalamic bursts originate from activation of the low threshold calcium cannels via a local feedback inhibition, exerted by the thalamic reticular neurons upon the relay neurons. This article, examines if this simple mechanism is sufficient to explain the distinctive properties of thalamic bursting as an effective relay mode. A minimal model of thalamic circuit composed of a retinal spike train, a relay neuron and a reticular neuron is simulated to generate the tonic and burst firing modes. The integrate-and-fire-or-burst model is used to simulate the neurons. After discriminating the burst events with criteria based on inter-spike-intervals, statistical indices show that the bursts of the minimal model are stereotypic events. The relation between the rate of bursts and the parameters of the input spike train demonstrates marked nonlinearities. Burst response is shown to be selective to spike-silence-spike sequences in the input spike train. Moreover, burst events represent the input more reliably than the tonic spike in a considerable range of the parameters of the model. In conclusion, many of the distinctive properties of thalamic bursts such as stereotypy, nonlinear dependence on the sensory stimulus, feature selectivity and reliability are reproducible in the minimal model. Furthermore, the minimal model predicts that while the bursts are more frequent in the spike train of the off-center X relay neurons (corresponding to off-center X retinal ganglion cells), they are more reliable when generated by the on-center ones (corresponding to on-center X ganglion cells).

Action Potentials↗