The P300 or P3, a late positive component of sensory evoked potentials, is said to reflect a variety of cognitive functions and to provide an objective index of information processing in normal and neurologically compromised individuals. An important issue in cognitive neuroscience has been the identification of the brain structures that generate it. However, extensive investigations conducted for that purpose and involving intracranial recordings and mapping of its scalp distribution have been inconclusive. Using magnetoencephalography (MEG) a method akin to traditional electrophysiology, but of greater spatial resolution we have recorded the magnetic equivalent of P3 to auditory stimuli and have localized its sources on the superior surface of the temporal lobe. We also found evidence that deeper sources (possibly thalamic) may contribute to its onset. These results lead to two general hypotheses: (a) That P3s are modality-specific and (b) that activation of modality-specific cortical regions is preceded by early thalamic activity. We propose to test these general hypotheses in a series of twelve experiments where P3s to rare and to unexpectedly missing auditory, visual and somatosensory stimuli will be obtained under two conditions. One will involve attention to stimuli resulting in a long latency P3, which is thought to reflect mostly higher order cognitive operations. The other will involve ignoring the stimuli, resulting in a shorter latency P3 associated with more basic sensory functions. The estimated sources of P3s obtained with the different stimulus modalities and conditions, projected onto individual magnetic resonance images (MRIs) will be used to answer whether P3s are modality-specific, whether they share an early thalamic origin and whether different structures generate P3s to the presence or absence of attended or incidentally registered unexpected environmental events.

National Institute of Health (NIH)
National Institute of Neurological Disorders and Stroke (NINDS)
Research Project (R01)
Project #
Application #
Study Section
Neurology A Study Section (NEUA)
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
University of Texas Medical Br Galveston
Schools of Medicine
United States
Zip Code
Zouridakis, G; Simos, P G; Breier, J I et al. (1998) Functional hemispheric asymmetry assessment in a visual language task using MEG. Brain Topogr 11:57-65
Simos, P G; Breier, J I; Zouridakis, G et al. (1998) Assessment of functional cerebral laterality for language using magnetoencephalography. J Clin Neurophysiol 15:364-72
Zouridakis, G; Simos, P G; Papanicolaou, A C (1998) Multiple bilaterally asymmetric cortical sources account for the auditory N1m component. Brain Topogr 10:183-9
Simos, P G; Breier, J I; Zouridakis, G et al. (1998) Identification of language-specific brain activity using magnetoencephalography. J Clin Exp Neuropsychol 20:706-22
Simos, P G; Basile, L F; Papanicolaou, A C (1997) Source localization of the N400 response in a sentence-reading paradigm using evoked magnetic fields and magnetic resonance imaging. Brain Res 762:29-39
Basile, L F; Brunder, D G; Tarkka, I M et al. (1997) Magnetic fields from human prefrontal cortex differ during two recognition tasks. Int J Psychophysiol 27:29-41
Basile, L F; Rogers, R L; Simos, P G et al. (1997) Magnetoencephalographic evidence for common sources of long latency fields to rare target and rare novel visual stimuli. Int J Psychophysiol 25:123-37
Papanicolaou, A C (1995) An introduction to magnetoencephalography with some applications. Brain Cogn 27:331-52
Tarkka, I M; Stokic, D S; Basile, L F et al. (1995) Electric source localization of the auditory P300 agrees with magnetic source localization. Electroencephalogr Clin Neurophysiol 96:538-45
Basile, L F; Rogers, R L; Bourbon, W T et al. (1994) Slow magnetic flux from human frontal cortex. Electroencephalogr Clin Neurophysiol 90:157-65

Showing the most recent 10 out of 12 publications