A feasibility study of an improved procedure for using EEG to detect brain responses to imagery instruction in patients with disorders of consciousness.

Anna Lisa Mangia,Marco Pirini,Angelo Cappello,Laura Simoncini,Lawrence M Ward

doi:10.1371/journal.pone.0099289

Abstract

One of the major concerns of recent studies is the correct discrimination between vegetative and minimally conscious state as the distinction between these two conditions has major implications for subsequent patient rehabilitation. In particular, it would be advantageous to establish communication with these patients. This work describes a procedure using EEG to detect brain responses to imagery instruction in patients with disorders of consciousness. Five healthy subjects and five patients with different disorders of consciousness took part in the study. A support vector machine classifier applied to EEG data was used to distinguish two mental tasks (Imagery Trial) and to detect answers to simple yes or no questions (pre-Communication Trial). The proposed procedure uses feature selection based on a nested-leave-one-out algorithm to reduce the number of electrodes required. We obtained a mean classification accuracy of 82.0% (SD 5.1%) for healthy subjects and 84.6% (SD 9.1%) for patients in the Imagery Trial, and a mean classification accuracy of 80.7% (SD 11.5%) for healthy subjects and 91.7% (SD 7.4%) for patients in the pre-Communication Trial. The subset of electrodes selected was subject and session dependent.

Highlights

Recent improvements in intensive care have led to an increase in the number of patients who survive severe head trauma, intracranial haemorrhage or non-traumatic anoxic brain injuries
Despite the very promising results obtained by these studies, functional magnetic resonance imaging (fMRI)-based applications remain challenging for many reasons: 1) high costs; 2) limited scanner availability; 3) the inactive state of these patients; 4) the frequent uncontrolled, involuntary movements inside the scanner; 5) the substantial physical stress to patients on transfer to the fMRI facility
The second aim of the study was to evaluate the reliability of a classification procedure to distinguish between the electrode activation patterns of the two mental states evoked by the two imagery tasks

Summary

Introduction

Recent improvements in intensive care have led to an increase in the number of patients who survive severe head trauma, intracranial haemorrhage or non-traumatic anoxic brain injuries. And colleagues developed an fMRI paradigm of reliable voluntary activation in response to an imagery task [4] They found two imagery tasks which elicit extremely reliable, robust and statistically distinguishable patterns of activation in specific regions of the brain: spatial navigation imagery, imagining moving from room to room in your own home, and motor imagery, imagining playing tennis. After this preliminary study, Owen and colleagues used Boly et al.’s paradigms to show that a patient who seemed to be entirely vegetative might be aware, since her blood oxygen-level was modulated by the various mental imagery tasks [5]. Metal implants, including plates and pins, which are common in most traumatically injured populations, rule out the use of fMRI

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