Cortical Function Mapping with Intracranial EEG - Quantitative EEG Analysis Methods and Clinical Applications - page 374

well as by functional neuroimaging studies [11]. Converging data from these studies
have demonstrated that the P3 and its component waveforms are generated by a
widely distributed network of cortical regions that collectively take part in detection
behavior. The P3a component, which is evoked by rare stimuli and likely represents
an orienting response to unexpected but behaviorally salient stimuli (e.g., to screech-
ing tires or a gunshot), is generated in dorsolateral prefrontal cortex, supramarginal
gyrus, and cingulate cortex (Figure 14.2) [12]. In contrast, the P3b component,
which is evoked by target stimuli during a voluntary detection task, is generated by
ventrolateral prefrontal cortex, superior temporal sulcus, posterior superior parietal
cortex, and medial temporal structures including hippocampus and perirhinal
regions.
Another cognitive task that has been studied extensively with iEEG is discrimi-
nation and identification of complex visual stimuli such as real or pictured objects,
faces, letters, or words. These tasks require processing within the functional-ana-
tomic domain known as the “what” stream of visual information processing in tem-
poral-occipital cortex. Although much has been learned about this system through
basic investigations in nonhuman primates, and subsequently through functional
neuroimaging studies in humans, human iEEG studies have provided vital informa-
tion about the spatiotemporal dynamics of information processing in the ventral
temporal-occipital stream [13-17].
iEEG studies of phase-locked responses have also yielded important insights
about more basic sensory evoked potentials. For example, iEEG studies have been
instrumental in determining the cortical generators of the somatosensory evoked
potential [18-20], as well as the somatotopic organization of somatosensory cortex
[19, 21-23]. Even the cortical networks responsible for pain perception have been
studied with iEEG [24, 25]. A number of studies have also explored the neural sub-
strates of a variety of ERPs elicited by functional activation of motor, premotor, and
supplementary motor cortex [26].

P3a generators
supramarginal g.

Dorsolateral prefrontal

Cingulate gyrus

Ventrolateral
prefrontal

Superior temporal
sulcus

Posterior superior
parietal

Medial temporal
(hippocampal
and perirhinal)

P3b generators

Figure 14.2 Summary of areas where P3a and P3b were generated by simple rare stimuli, according to
recordings at a cumulative ~4,000 iEEG sites. Lateral (left) and medial (right) views are shown. ( From: [12]. ©
1998 Elsevier Science Ireland Ltd. Reprinted with permission.)