Pharmacoresistant epilepsy is a common neurological disorder in which increased neuronal intrinsic excitability and synaptic excitation lead to pathologically synchronous behavior in the brain. In the majority of experimental and theoretical epilepsy models, epilepsy is associated with reduced inhibition in the pathological neural circuits, yet effects of intrinsic excitability are usually not explicitly analyzed. Here we present a novel neural mass model that includes intrinsic excitability in the form of spike-frequency adaptation in the excitatory population. We validated our model using local field potential data recorded from human hippocampal/subicular slices. We found that synaptic conductances and slow adaptation in the excitatory population both play essential roles for generating seizures and pre-ictal oscillations. Using bifurcation analysis, we found that transitions towards seizure and back to the resting state take place via Andronov-Hopf bifurcations. These simulations therefore suggest that single neuron adaptation as well as synaptic inhibition are responsible for orchestrating seizure dynamics and transition towards the epileptic state.
In this study, we investigated the effect of transcranial alternating current stimulation (tACS) on decision making under risk and executive control in humans. Stimulation was delivered online at 5, 10, 20, and 40 Hz on the left and right DLPFC while subjects performed a modified risky decision making task. This task allowed subjects to voluntarily switch between risky and safe options associated with potential gains or losses while simultaneously measuring the cognitive control component (voluntary switching) of decision making. Our results revealed a frequency- and hemisphere-specific effect of 20Hz tACS delivered on the left DLPFC that significantly increased risk-taking. These results suggest a modulatory role of 20 Hz neural oscillations on the left DLPFC in risk-taking perhaps by activating the brain’s reward system.
Transcranial direct current stimulation (tDCS) is a promising tool for modulation of learning and memory, allowing to transiently change cortical excitability of specific brain regions with physiological and behavioral outcomes. A detailed exploration of factors that can moderate tDCS effects on episodic long-term memory (LTM) is of high interest due to the clinical potential for patients with traumatic or pathological memory deficits and with cognitive impairments. This commentary discusses findings by Marián et al. (2018) recently published in Cortex within a broad context of brain stimulation in memory research.