Depth electrode neurofeedback with a virtual reality interface

Invasive brain–computer interfaces (BCI) provide better signal quality in terms of spatial localization, frequencies and signal/noise ratio, in addition to giving access to deep brain regions that play important roles in cognitive or affective processes. Despite some anecdotal attempts, little work has explored the possibility of integrating such BCI input into more sophisticated interactive systems like those which can be developed with game engines. In this article, we integrated an amygdala depth electrode recorder with a virtual environment controlling a virtual crowd. Subjects were asked to down regulate their amygdala using the level of unrest in the virtual room as feedback on how successful they were. We report early results which suggest that users adapt very easily to this paradigm and that the timing and fluctuations of amygdala activity during self-regulation can be matched by crowd animation in the virtual room. This suggests that depth electrodes could also serve as high-performance affective interfaces, notwithstanding their strictly limited availability, justified on medical grounds only

The Priority Structure of Bank Regulatory Capital: The Case of Subordinated Debt

The aftermath of a crisis often brings reflections on the adequacy of regulatory capital against financial shocks. Accordingly, succeeding regulatory interventions focus on strengthening the resilience of the banking system by improving the quality and quantity of capital, and subordinated debt (sub-debt) remains key to these reforms. Whether, however, the regulatory motive underpins the decision of banks to issue sub-debt is unclear. Moreover, the perceptions of shareholders on the regulatory function of sub-debt are less understood. This thesis attempts to answer these questions by first reviewing other roles of sub-debt then testing if regulation drives its issuance and finally revealing shareholder incentives that weaken its regulatory function. Contrasting capital requirement motives with other explanations, and accounting for equity issuance, we find that banks issue sub-debt primarily to improve their regulatory capital buffer. While a few non-regulatory factors, related to easier entry conditions to debt market, influence the issuance decision, their economic impact is smaller than the impact of the buffer. By exploring how variations in tail risk and size influence the sub-debt and equity issuance decisions by banks with low buffers, we show that issuance choices do not reflect risk-shifting incentives. Next, we review shareholders’ perceptions of the regulatory value of sub-debt vis-a-vis the risk-shifting and wealth-expropriation incentives associated with senior debt by comparing the reaction of stocks to these security announcements. We find that senior debt incentives are more valuable than the regulatory benefit of sub-debt. Contrary to regulatory expectations, announcement of sub-debt (capital-improving) offers are valueless even when undertaken by risky or less-capitalized banks; rather, senior debt offered by these vulnerable banks generate significant shareholder value. Pursuant to these risk-shifting motives, senior debt issuers get riskier post-issuance. These findings suggest that the broader debt priority structure harbours perverse incentives that dilute the regulatory effectiveness of sub-debt

Characterization of hippocampal subregional cross-frequency associations, and the effect of Deep Brain Stimulation on memory performance in Humans

Deep brain stimulation (DBS) of the Medial Temporal Lobe (MTL) in humans has offered promise for improving hippocampal-dependent learning and memory, yet little is known about how it modulates the electrophysiological mechanisms associated with hippocampal communication. Here, we explore the role of theta-gamma coupling, a putative entorhinal- hippocampal organizing mechanism, in successful memory formation, while human subjects implanted with intracranial electrodes engage in hippocampal-dependent memory tasks. Our results suggest that entorhinal area DBS, previously shown to be associated with memory enhancement, also results in substantial coupling of theta and gamma oscillations within the hippocampus, suggesting a possible mechanism for stimulation related memory enhancement. Further, we address hippocampal cross-frequency dynamics during encoding and retrieval at the level of hippocampal subfields, showing that CA1 theta high-gamma coupling increases preferentially during encoding of subsequently recollected objects, while both CA1 and CA2- 3-DG exhibit memory specific cross-frequency coupling changes during retrieval. Finally, we perform a multi-task analysis to assess how generalizable is the effect of DBS across multiple entorhinal stimulation targets, memory modalities, and stimulation protocols; our results show that stimulation of entorhinal white matter enhances declarative memory encoding

Characterization of hippocampal subregional cross-frequency associations, and the effect of Deep Brain Stimulation on memory performance in Humans

Deep brain stimulation (DBS) of the Medial Temporal Lobe (MTL) in humans has offered promise for improving hippocampal-dependent learning and memory, yet little is known about how it modulates the electrophysiological mechanisms associated with hippocampal communication. Here, we explore the role of theta-gamma coupling, a putative entorhinal- hippocampal organizing mechanism, in successful memory formation, while human subjects implanted with intracranial electrodes engage in hippocampal-dependent memory tasks. Our results suggest that entorhinal area DBS, previously shown to be associated with memory enhancement, also results in substantial coupling of theta and gamma oscillations within the hippocampus, suggesting a possible mechanism for stimulation related memory enhancement. Further, we address hippocampal cross-frequency dynamics during encoding and retrieval at the level of hippocampal subfields, showing that CA1 theta high-gamma coupling increases preferentially during encoding of subsequently recollected objects, while both CA1 and CA2- 3-DG exhibit memory specific cross-frequency coupling changes during retrieval. Finally, we perform a multi-task analysis to assess how generalizable is the effect of DBS across multiple entorhinal stimulation targets, memory modalities, and stimulation protocols; our results show that stimulation of entorhinal white matter enhances declarative memory encoding

Augmenting hippocampal-prefrontal neuronal synchrony during sleep enhances memory consolidation in humans.

Memory consolidation during sleep is thought to depend on the coordinated interplay between cortical slow waves, thalamocortical sleep spindles and hippocampal ripples, but direct evidence is lacking. Here, we implemented real-time closed-loop deep brain stimulation in human prefrontal cortex during sleep and tested its effects on sleep electrophysiology and on overnight consolidation of declarative memory. Synchronizing the stimulation to the active phases of endogenous slow waves in the medial temporal lobe (MTL) enhanced sleep spindles, boosted locking of brain-wide neural spiking activity to MTL slow waves, and improved coupling between MTL ripples and thalamocortical oscillations. Furthermore, synchronized stimulation enhanced the accuracy of recognition memory. By contrast, identical stimulation without this precise time-locking was not associated with, and sometimes even degraded, these electrophysiological and behavioral effects. Notably, individual changes in memory accuracy were highly correlated with electrophysiological effects. Our results indicate that hippocampo-thalamocortical synchronization during sleep causally supports human memory consolidation

Theta-burst microstimulation in the human entorhinal area improves memory specificity.

The hippocampus is critical for episodic memory, and synaptic changes induced by long-term potentiation (LTP) are thought to underlie memory formation. In rodents, hippocampal LTP may be induced through electrical stimulation of the perforant path. To test whether similar techniques could improve episodic memory in humans, we implemented a microstimulation technique that allowed delivery of low-current electrical stimulation via 100 μm-diameter microelectrodes. As thirteen neurosurgical patients performed a person recognition task, microstimulation was applied in a theta-burst pattern, shown to optimally induce LTP. Microstimulation in the right entorhinal area during learning significantly improved subsequent memory specificity for novel portraits; participants were able both to recognize previously-viewed photos and reject similar lures. These results suggest that microstimulation with physiologic level currents-a radical departure from commonly used deep brain stimulation protocols-is sufficient to modulate human behavior and provides an avenue for refined interrogation of the circuits involved in human memory

Theta-Burst Microstimulation in the Human Entorhinal Area Improves Memory Specificity

The hippocampus is critical for episodic memory, and synaptic changes induced by long-term potentiation (LTP) are thought to underlie memory formation. In rodents, hippocampal LTP may be induced through electrical stimulation of the perforant path. To test whether similar techniques could improve episodic memory in humans, we implemented a microstimulation technique that allowed delivery of low-current electrical stimulation via 100 μm-diameter microelectrodes. As thirteen neurosurgical patients performed a person recognition task, microstimulation was applied in a theta-burst pattern, shown to optimally induce LTP. Microstimulation in the right entorhinal area during learning significantly improved subsequent memory specificity for novel portraits; participants were able both to recognize previously-viewed photos and reject similar lures. These results suggest that microstimulation with physiologic level currents—a radical departure from commonly used deep brain stimulation protocols—is sufficient to modulate human behavior and provides an avenue for refined interrogation of the circuits involved in human memory

Stimulation of the right entorhinal white matter enhances visual memory encoding in humans.

BackgroundWhile deep brain stimulation has been successful in treating movement disorders, such as in Parkinson's disease, its potential application in alleviating memory disorders is inconclusive.Objective/hypothesisWe investigated the role of the location of the stimulating electrode on memory improvement and hypothesized that entorhinal white versus gray matter stimulation would have differential effects on memory.MethodsIntracranial electrical stimulation was applied to the entorhinal area of twenty-two participants with already implanted electrodes as they completed visual memory tasks.ResultsWe found that stimulation of right entorhinal white matter during learning had a beneficial effect on subsequent memory, while stimulation of adjacent gray matter or left-sided stimulation was ineffective. This finding was consistent across three different visually guided memory tasks.ConclusionsOur results highlight the importance of precise stimulation site on modulation of human hippocampal-dependent memory and suggest that stimulation of afferent input into the right hippocampus may be an especially promising target for enhancement of visual memory