LPC subcomponents in a long-ISI dishabituation task

The Late Positive Complex (LPC) of the event-related potential

(ERP) has long been considered a central nervous system index of the

orienting reflex (OR). Previous studies have found that when

examined as a single ERP component, the LPC demonstrates habituation,

and reflects stimulus characteristics that are associated with the

OR (novelty, intensity, significance). However, a growing body of

evidence suggests that the LPC is not simply a unitary complex. It has

been shown that the LPC is composed of several distinct subcomponents,

each with different topographic distributions and sensitivities to

a variety of stimulus characteristics. Our previous work has aimed at

systematically disentangling these subcomponents of the LPC in the

OR context by employing a dishabituation paradigm with an 8 s

stimulus onset asynchrony (SOA). In the present study, we aimed to

extend our previous findings by exploring LPC subcomponents in a

long-interstimulus interval (ISI) dishabituation task. Twenty four

university students completed an auditory dishabituation task whilst

their electrodermal and electroencephalographic activity was recorded.

The task consisted of two counterbalanced blocks: indifferent,

in which there were no task requirements; and significant, in which

participants were instructed to count the stimuli. Stimuli consisted of

1000 and 1500 Hz counterbalanced (standard, deviant) 60 dB tones

that were separated by a random SOA of 12–15 s and delivered in the

following sequence: 10 standards, 1 deviant, 2–4 standards. Skin

conductance responses (SCRs) were extracted for each subject and

each trial. Single-trial EOG-corrected ERPs from 32-sites were

submitted to principal components analysis, from which five identifiable

LPC subcomponentswere extracted:Novelty P3, P3a, P3b, and two

SlowWaves (SW1 and SW2). As expected, SCR behaved as an OR index,

demonstrating habituation (decrement, recovery, dishabituation) and

larger magnitude responses to significant compared to indifferent

stimuli. Novelty P3 evidenced topography-specific decrement over

trials, a main effect of recovery, but little evidence of dishabituation.

P3a and P3b also showed topographic decrement, but topographyspecific

recovery and dishabituation were only apparent for P3a.

Neither of the two SWs demonstrated habituation, but SW2 did

evidence a main effect of condition. The LPC subcomponents identified

here did not demonstrate a uniform response-pattern across trials and

conditions. These findings suggest that the LPC represents a variety of

distinct neural processes, and support the notion that the LPC should

be examined further as a series of subcomponents, rather than a global

complex. Importantly, our LPC findings differed from that of our

previous work with shorter ISIs, with weaker trials effects for longer

ISIs. Taken together, these findings suggest that the mechanisms

underlying habituation of ERPs may be less functional when repetitive

stimuli are separated by longer ISIs.