Laskaris mining information_neuroinformatics

[ IEEE SP Magazine, May 2004 ]

N. Laskaris,
S. Fotopoulos,
A. Ioannides

ENTER-2001

new tools
for Mining Information from
multichannel encephalographic recordings

& applications

What is Data Mining ?

How is it applied ?

Why is it useful ?
What is the difficulty with single trials ?
How can Data Mining help ?

Which are the algorithmic steps ?

Is there a simple example ?

Is there a more elaborate example ?

What has been the gain ?
Where one can learn more ?

What is Data Mining
&
Knowledge Discovery in databases ?

Data Mining
is “the data-driven discovery and
modeling of hidden patterns in large
volumes of data.”
It is a multidisciplinary field,
borrowing and enhancing ideas from diverse areas such
as statistics, image understanding, mathematical
optimization, computer vision, and pattern recognition.

It is the process of nontrivial extraction of implicit,
implicit
previously unknown, and
potentially useful information from voluminous data.
data

How is it applied in the context of
multichannel
encephalographic recordings ?

Studying Brain’s self-organization
by monitoring the dynamic pattern formation
reflecting neural activity

3
Why is it
a potentially valuable methodology
for analyzing
Event-Related recordings ?

The traditional -It blends everything
approach is based on happened during
identifying peaks
the recording
in the averaged signal

The analysis of
Event-Related Dynamics
aims at understanding
the real-time processing of a stimulus
performed in the cortex
and demands tools
able to deal with Multi-Trial data

4

What is the difficulty
in analyzing
Single-Trial responses ?

At the single-trial level,
we are facing
Complex Spatiotemporal Dynamics

5
How can Data Mining help
to circumvent this complexity
and reveal
the underlying brain mechanisms ?

directed queries are formed
in the Single-Trial data
which are then summarized
using a very limited vocabulary
of information granules
that are easily understood,
accompanied by well-defined semantics
and help express relationships existing in the data

The information abstraction
is usually accomplished
via clustering techniques

and followed by a proper visualization scheme
that can readily spot interesting events
and trends in the experimental data.

- Semantic Maps

The Cartography of neural function
results in a topographical representation
of response variation
and enables the virtual navigation
in the encephalographic database

6

Which are
the intermediate
algorithmic steps ?

A Hybrid approach

Pattern Analysis
& Graph Theory

Step_
the spatiotemporal dynamics are decomposed

Design of the spatial filter used to extract
the temporal patterns conveying
the regional response dynamics

Step_
Pattern Analysis
of the extracted ST-patterns
Clustering &
Vector Quantization
Feature Embedding
extraction in Feature Space
Minimal Spanning Tree
of the codebook
Interactive Study
of pattern variability
Orderly presentation
of response variability
MST-ordering
of the code vectors

Laskaris mining information_neuroinformatics

Step_
Within-group Analysis
of regional response dynamics

-

Step_
of multichannel single-trial signals

Step_
of single-trial MFT-solutions

7

Is there
a simple example?

[ Laskaris & Ioannides, Clin. Neurophys., 2001 ]

120 trials,
Repeated stimulation binaural-stimulation
[ 1kHz tones, 0.2s, 45 dB ],
ISI: 3sec, passive listening

Task : to ‘‘explain’’
the averaged M100-response

The M100-peak emerges from
the stimulus-induced phase-resetting

Phase reorganization
of the ongoing brain waves

8

Is there
a more elaborate example?

[ Laskaris et al., NeuroImage, 2003 ]

A study of
global firing patterns

Their relation
with localized sources

240 trials, pattern reversal,
4.5 deg , ISI: 0.7 sec,
passive viewing

Single-Trial data
in unorganized format

Single-Trial data summarized
via ordered prototypes
reflecting the variability
of regional response dynamics

‘‘The ongoing activity
before the stimulus-onset
is functionally coupled
with the subsequent
regional response’’

Polymodal Parietal Areas
BA5 & BA7
are the major sources
of the observed variability

Regional vs Local
response dynamics :

There is relationship
between
N70m-response variability
and activity
in early visual areas.

9
What has been the lesson,
so far,
from the analysis
of Event-Related Dynamics ?

The ‘‘dangerous’’
equation

Where one can learn more
about Mining Information
from encephalographic recordings ?

//www.hbd.brain.riken.jp
symposium: MEG in psychiatry
(AUD4, Monday, 9.00 )

Laskaris mining information_neuroinformatics

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