Updating p300 an integrative theory of p3a and p3b
Loud tones occurred with a probability of .9, .5, or .1, while the soft tones occurred with complementary probability.In addition, subjects completed blocks of stimuli under instruction to count the number of loud tones, count the number of soft tones, or ignore the tones and quietly read.At the time, several researchers suggested that there needed to be active attention towards the target stimuli in order to elicit a P300, in part because stimuli that were ignored resulted in a P300 with a smaller amplitude or no P300 at all.On the other hand, some research had shown that subjects exhibit a P300 to unpredictable stimuli in an ongoing repetitive series of stimuli, even when the stimuli were classified as irrelevant and subjects were asked to ignore them while completing another task (i.e. It was intriguing that you could elicit a P300 in conditions with active attention and those of non-attention.estless legs syndrome may be a condition of impaired CNS dopamine function. Dopamine deficiency is associated with bradykinesia and impaired attention (e.g., Parkinson's disease and attention deficit disorder), and dopamine restoration or excess (e.g., treatment of patients with Parkinson's disease with L-3,4-dihydroxyphenlyalanine [L-dopa] and of patients with attention deficit disorder with amphetamine) is associated with normal or excessive movement and with improved attention. Comorbid patients showed both anxiety-related and depression-related activity.
When an infrequently presented "distracter" stimulus randomly occurs (e.g., a large checkerboard pattern), the attentional focus induced by the discrimination task is disrupted and produces a P3a potential that has its maximum amplitude over frontal-central areas of the scalp; the target stimulus elicits the P3b potential over the parietal areas.
The P3b is a subcomponent of the P300, an event-related potential (ERP) component that can be observed in human scalp recordings of brain electrical activity.
The P3b is a positive-going amplitude (usually relative to a reference behind the ear or the average of two such references) peaking at around 300 ms, though the peak will vary in latency (delay between stimulus and response) from 250–500 ms or later depending upon the task.
The P3a has been associated with brain activity related to the engagement of attention (especially orienting and involuntary shifts to changes in the environment) and the processing of novelty.
In 1975 Squires and colleagues conducted a study attempting to resolve some of the questions surrounding what neural process the P300 reflects.
This study examined the impact of depressive disorders, anxiety disorders and the comorbidity of these disorders on the regional electrophysiological features of brain activity.