42 research outputs found
Simultaneous embedding of multiple attractor manifolds in a recurrent neural network using constrained gradient optimization
The storage of continuous variables in working memory is hypothesized to be
sustained in the brain by the dynamics of recurrent neural networks (RNNs)
whose steady states form continuous manifolds. In some cases, it is thought
that the synaptic connectivity supports multiple attractor manifolds, each
mapped to a different context or task. For example, in hippocampal area CA3,
positions in distinct environments are represented by distinct sets of
population activity patterns, each forming a continuum. It has been argued that
the embedding of multiple continuous attractors in a single RNN inevitably
causes detrimental interference: quenched noise in the synaptic connectivity
disrupts the continuity of each attractor, replacing it by a discrete set of
steady states that can be conceptualized as lying on local minima of an
abstract energy landscape. Consequently, population activity patterns exhibit
systematic drifts towards one of these discrete minima, thereby degrading the
stored memory over time. Here we show that it is possible to dramatically
attenuate these detrimental interference effects by adjusting the synaptic
weights. Synaptic weight adjustments are derived from a loss function that
quantifies the roughness of the energy landscape along each of the embedded
attractor manifolds. By minimizing this loss function, the stability of states
can be dramatically improved, without compromising the capacity.Comment: To be presetned at the Thirty-seventh Conference on Neural
Information Processing Systems (NeurIPS 2023
An Efficient Coding Theory for a Dynamic Trajectory Predicts non-Uniform Allocation of Grid Cells to Modules in the Entorhinal Cortex
Grid cells in the entorhinal cortex encode the position of an animal in its
environment using spatially periodic tuning curves of varying periodicity.
Recent experiments established that these cells are functionally organized in
discrete modules with uniform grid spacing. Here we develop a theory for
efficient coding of position, which takes into account the temporal statistics
of the animal's motion. The theory predicts a sharp decrease of module
population sizes with grid spacing, in agreement with the trends seen in the
experimental data. We identify a simple scheme for readout of the grid cell
code by neural circuitry, that can match in accuracy the optimal Bayesian
decoder of the spikes. This readout scheme requires persistence over varying
timescales, ranging from ~1ms to ~1s, depending on the grid cell module. Our
results suggest that the brain employs an efficient representation of position
which takes advantage of the spatiotemporal statistics of the encoded variable,
in similarity to the principles that govern early sensory coding.Comment: 23 pages, 5 figures. Supplemental Information available from the
authors on request. A previous version of this work appeared in abstract form
(Program No. 727.02. 2015 Neuroscience Meeting Planner. Chicago, IL: Society
for Neuroscience, 2015. Online.
Microemboli monitoring by trans-cranial doppler in patient with acute cardioemboliogenic stroke due to atrial myxoma
This is the first reported attempt to examine the emboliogenic potential of cardiac myxoma in patients with acute stroke through the monitoring of microembolic signals (MES) by transcranial doppler. A 43-year old woman was brought to the emergency department because of acute onset of generalized tonic-clonic seizures and left hemiplegia. A CT scan of the brain demonstrated a large acute infraction in the territory of the right middle cerebral artery (MCA) and another smaller one in the territory of the posterior cerebral artery on the same side. Trans-cranial doppler (TCD) microemboli monitoring did not reveal MES. Transesophagial echocardiography (TEE) identified a 5 cm left atrial mass, which was highly suspected to be an atrial myxoma attached to the interatrial septum and prolapsed through the mitral valve. After the TEE results were obtained, another TCD monitoring was performed. Again, there were no MES found in either of the MCAs
Left Ventricular Systolic Dysfunction Due to Atrial Fibrillation: Clinical and Echocardiographic Predictors
Background: Diagnosis of AF-induced cardiomyopathy can be challenging and relies on ruling out other causes of cardiomyopathy and, after restoration of sinus rhythm, recovery of left ventricular (LV) function. The aim of this study was to identify clinical and echocardiographic predictors for developing cardiomyopathy with systolic dysfunction in patients with atrial tachyarrhythmia. Methods: This retrospective study was conducted in a large tertiary care centre and compared patients who experienced deterioration of LV ejection fraction (EF) during paroxysmal AF, demonstrated by precardioversion transoesophageal echocardiography with patients with preserved LV function during AF. All patients had documented preserved LVEF at baseline (EF >50%) while in sinus rhythm. Results: Of 482 patients included in the final analysis, 80 (17%) had reduced and 402 (83%) had preserved LV function during the precardioversion transoesophageal echocardiography. Patients with reduced LVEF were more likely to be men and to have a more rapid ventricular response during AF or atrial flutter (AFL). A history of prosthetic valves was also identified as a risk factor for reduced LVEF. Patients with reduced LVEF also had higher incidence of tricuspid regurgitation and right ventricular dysfunction. Conclusion: In ‘real-world’ experience, male patients with rapid ventricular response during paroxysmal AF or AFL are more prone to LVEF reduction. Patients with prosthetic valves are also at risk for LVEF reduction during AF/AFL. Finally, tricuspid regurgitation and right ventricular dysfunction may indicate relatively long-standing AF with an associated reduction in LVEF
CONCORDANCE OF VALVE AREA AND PRESSURE GRADIENT IN PATIENTS WITH AORTIC VALVE STENOSIS AND PRESERVED LEFT VENTRICULAR EJECTION FRACTION
CONCORDANCE OF VALVE AREA AND PRESSURE GRADIENT IN PATIENTS WITH AORTIC VALVE STENOSIS AND PRESERVED LEFT VENTRICULAR EJECTION FRACTION
Recommended from our members
Pseudoaneurysm of the mitral-aortic intervalvular fibrosa following aortic valve replacement - diagnosis and dynamic evaluation with multidetector CT and transesophageal echocardiography
Sixteen-slice multidetector CT findings of a pulsatile pseudoaneurysm of the mitral-aortic intervalvular fibrosa, in a woman following aortic valve replacement, are presented. Multidetector CT depicted the pseudoaneurysm and enabled dynamic evaluation of its lumen through the cardiac cycle, documenting expansion during systole and almost complete collapse during diastole. This case illustrates the capabilities of multidetector cardiac CT in the evaluation of aortic valve pathology