The auditory oddball paradigm revised to improve bedside detection of consciousness in behaviorally unresponsive patients

Abstract

Active paradigms requiring subjects to engage in a mental task on request have been developed to detect consciousness in behaviorally unresponsive patients. Using auditory ERPs, the active condition consists in orienting patient's attention toward oddball stimuli. In comparison with passive listening, larger P300 in the active condition identifies voluntary processes. However, contrast between these two conditions is usually too weak to be detected at the individual level. To improve test sensitivity, we propose as a control condition to actively divert the subject's attention from the auditory stimuli with a mental imagery task that has been demonstrated to be within the grasp of the targeted patients: navigate in one's home. Twenty healthy subjects were presented with a two-tone oddball paradigm in the three following condition: (a) passive listening, (b) mental imagery, (c) silent counting of deviant stimuli. Mental imagery proved to be more efficient than passive listening to lessen P300 response to deviant tones as compared with the active counting condition. An effect of attention manipulation (oriented vs. diverted) was observed in 19/20 subjects, of whom 18 showed the expected P300 effect and 1 showed an effect restricted to the N2 component. The only subject showing no effect also proved insufficient engagement in the tasks. Our study demonstrated the efficiency of diverting attention using mental imagery to improve the sensitivity of the active oddball paradigm. Using recorded instructions and requiring a small number of electrodes, the test was designed to be conveniently and economically used at the patient's bedside.

Potential Mechanisms for the Ketamine-Induced Reduction of P3b Amplitudes

“…This finding suggests that the processing of such distractors is more strongly engaged in harder target detection tasks. In contrast, when rare, task-irrelevant auditory stimuli had to be ignored and were presented during a primary visual task, the (early) P3a amplitude to these auditory stimuli decreased with increasing difficulty in the primary task or as compared to conditions without a visual task (Harmony et al, 2000; Restuccia et al, 2005; Yucel et al, 2005; Muller-Gass et al, 2006; Zhang et al, 2006; Allison and Polich, 2008; SanMiguel et al, 2008; Sculthorpe et al, 2008; Lv et al, 2010; Miller et al, 2011; Dyke et al, 2015; Molloy et al, 2015; Morlet et al, 2017; Tusch et al, 2017, Table 1B). Even though the P3a in passive oddball tasks is considered to reflect an involuntary attention switch in response to sound deviance (Näätänen, 1990; Escera et al, 2000), the P3a is stronger when participants attend the auditory stimuli (Wronka et al, 2008).…”

A Signature of Passivity? An Explorative Study of the N3 Event- Related Potential Component in Passive Oddball Tasks

“…Moreover, if this hypothesis is true, N3 might also be found in some active oddball experiments, e.g., when the experimental instruction was (intentionally or not) formulated with less precision. For example, N3 in active oddball was recorded in Polich (1989) and Kayser et al (1998), and in Mueller et al (2008) it was even larger in the active than passive paradigm, which is in strong contrast with the data of Erlbeck et al (2014), Brown et al (2015) and Morlet et al (2017). However, the hypothesis about a link between the active N3 and the precision of the experimental instruction can only be tested in a systematic review of the voluminous literature about ERPs in active oddball, which should be a subject of a separate study.…”

“…If this hypothesis is true, further experiments can be designed to vary the precision of the meaning of presented stimuli. A starting paradigm may be the design of Erlbeck et al (2014) or Morlet et al (2017) who employed an active condition (attention to the stimuli), a distraction condition (attention away from the stimuli), and a passive condition (free attention). However, future experiments on this basis should employ more gradual conditions, such as attentional tasks with high and low motivation (assuming that motivation mobilizes attentional resources), instructions to pay attention to the stimuli without any overt or covert response, or just presentation of stimuli without any instruction.…”

“…Several control studies aimed at the development of the passive oddball paradigm for severely brain damaged patients confirmed the presence of P3b, but the waveforms presented in these studies also indicated a later negative deflection with a peak latency between 400 and 500 ms. Bostanov and Kotchoubey (2006) used a continuous wavelet transform and clearly showed this wave in both time and time-frequency analyzed responses. Erlbeck et al (2014) and Morlet et al (2017) directly compared ERPs in the oddball paradigm (a) with an active instruction to respond to stimuli, (b) with active distraction of attention away from stimuli, and (c) with mind wandering (Morlet et al, 2017) or without any task (Erlbeck et al, 2014). Both studies showed a clear negativity following P3 to deviant stimuli in the last condition, but not in the other two.…”

A framework for the extended monitoring of levels of cognitive function in unresponsive patients

“…It is important to reiterate that the only instruction given to the participants in the first cohort was that they need not pay attention to the stimuli. As has been noted elsewhere (see [ 24 ] for a review of N400 and attention, and [ 54 ] for a discussion of the P300 and attention), not attending to the stimuli can significantly reduce the amplitude of an ERP response. As was seen in from the first cohort, the most robust responses were generated when the stimuli were salient and contextually different enough to attract attention regardless of whether the stimuli were being attended to explicitly or not.…”