Biomedical subjects

A Effern

Publications and source records attributed to A Effern.

4 recordsLinked to original sources

PubMed2001

Nonlinear noise reduction using reference data.

We introduce a method to clean uncorrelated deterministic and stochastic noise components from time series. It combines recently developed techniques for nonlinear projection with properties of the wavelet transform to extract noise in state space. The method requires that time series are generated by a dynamical system which is at least approximately deterministic and that they are recorded together with a reference signal. Its efficiency was tested on both simulated signals and measured magnetic fields of the heart. Convincing results are obtained even at low signal-to-noise ratios.

Journal Article↗

PubMed2000

Single trial analysis of event related potentials: non-linear de-noising with wavelets.

We present and apply a method for single trial analysis of event related potentials (ERPs) that combines techniques from non-linear time series analysis with the wavelet transform. For this method, convincing results have already been achieved for simulated data as well as for intracranially recorded ERPs (Physica D 140 (2000) 257). However, ERPs are affected by a variety of external and internal experimental parameters, which makes the appropriate configuration of single trial analysis difficult. Thus, several pitfalls may occur in realistic applications. In this paper, we applied the method of non-linear de-noising with wavelets to both intra- and extracranially recorded ERPs, and show examples of how and where this single trial analysis can be used to obtain additional information on dynamic neural processes.

Brain↗

PubMed2000

Time adaptive denoising of single trial event-related potentials in the wavelet domain.

We present a new wavelet-based method for single trial analysis of transient and time variant event-related potentials (ERPs). Expecting more accurate filter settings than achieved by other techniques (low-pass filter, a posteriori Wiener filter, time invariant wavelet filter), ERPs were initially balanced in time. By simulation, better filter performance could be established for test signals contaminated with either white noise or isospectral noise. To provide an example of real application, the method was applied to limbic P300 potentials (MTL-P300). As a result, variance of single trial MTL-P300s decreased, without restricting the corresponding mean. The proposed method can be regarded as an alternative for single-trial ERP analysis.

Artifacts↗

PubMed1999

Real-time tracking of memory formation in the human rhinal cortex and hippocampus.

A fundamental question about human memory is which brain structures are involved, and when, in transforming experiences into memories. This experiment sought to identify neural correlates of memory formation with the use of intracerebral electrodes implanted in the brains of patients with temporal lobe epilepsy. Event-related potentials (ERPs) were recorded directly from the medial temporal lobe (MTL) as the patients studied single words. ERPs elicited by words subsequently recalled in a memory test were contrasted with ERPs elicited by unrecalled words. Memory formation was associated with distinct but interrelated ERP differences within the rhinal cortex and the hippocampus, which arose after about 300 and 500 milliseconds, respectively. These findings suggest that declarative memory formation is dissociable into subprocesses and sequentially organized within the MTL.

Adult↗