Showing papers by "Gregory McCarthy published in 1999"

Electrophysiological Studies of Human Face Perception. I: Potentials Generated in Occipitotemporal Cortex by Face and Non-face Stimuli

Abstract: This and the following two papers describe event-related potentials (ERPs) evoked by visual stimuli in 98 patients in whom electrodes were placed directly upon the cortical surface to monitor medically intractable seizures. Patients viewed pictures of faces, scrambled faces, letter-strings, number-strings, and animate and inanimate objects. This paper describes ERPs generated in striate and peristriate cortex, evoked by faces, and evoked by sinusoidal gratings, objects and letter-strings. Short-latency ERPs generated in striate and peristriate cortex were sensitive to elementary stimulus features such as luminance. Three types of face-specific ERPs were found: (i) a surface-negative potential with a peak latency of approximately 200 ms (N200) recorded from ventral occipitotemporal cortex, (ii) a lateral surface N200 recorded primarily from the middle temporal gyrus, and (iii) a late positive potential (P350) recorded from posterior ventral occipitotemporal, posterior lateral temporal and anterior ventral temporal cortex. Face-specific N200s were preceded by P150 and followed by P290 and N700 ERPs. N200 reflects initial face-specific processing, while P290, N700 and P350 reflect later face processing at or near N200 sites and in anterior ventral temporal cortex. Face-specific N200 amplitude was not significantly different in males and females, in the normal and abnormal hemisphere, or in the right and left hemisphere. However, cortical patches generating ventral face-specific N200s were larger in the right hemisphere. Other cortical patches in the same region of extrastriate cortex generated grating-sensitive N180s and object-specific or letter-string-specific N200s, suggesting that the human ventral object recognition system is segregated into functionally discrete regions.

Electrophysiological Studies of Human Face Perception. II: Response Properties of Face-specific Potentials Generated in Occipitotemporal Cortex

Abstract: In the previous paper the locations and basic response properties of N200 and other face-specific event-related potentials (ERPs) were described In this paper responsiveness of N200 and related ERPs to the perceptual features of faces and other images was assessed N200 amplitude did not vary substantially, whether evoked by colored or grayscale faces; normal, blurred or line-drawing faces; or by faces of different sizes Human hands evoked small N200s at face-specific sites, but evoked hand-specific ERPs at other sites Cat and dog faces evoked N200s that were 73% as large as to human faces Hemifield stimulation demonstrated that the right hemisphere is better at processing information about upright faces and transferring it to the left hemisphere, whereas the left hemisphere is better at processing information about inverted faces and transferring it to the right hemisphere N200 amplitude was largest to full faces and decreased progressively to eyes, face contours, lips and noses viewed in isolation A region just lateral to face-specific N200 sites was more responsive to internal face parts than to faces, and some sites in ventral occipitotemporal cortex were face-partspecific Faces with eyes averted or closed evoked larger N200s than those evoked by faces with eyes forward N200 amplitude and latency were affected by the joint effects of eye and head position in the right but not in the left hemisphere Full and three-quarter views of faces evoked larger N200s than did profile views The results are discussed in relation to behavioral studies in humans and single-cell recordings in monkeys

Electrophysiological Studies of Human Face Perception. III: Effects of Top-down Processing on Face-specific Potentials

Abstract: This is the last in a series of papers dealing with intracranial event-related potential (ERP) correlates of face perception. Here we describe the results of manipulations that may exert top-down influences on face recognition and face-specific ERPs, and the effects of cortical stimulation at face-specific sites. Ventral face-specific N200 was not evoked by affective stimuli; showed little or no habituation; was not affected by the familiarity or unfamiliarity of faces; showed no semantic priming; and was not affected by face-name learning or identification. P290 and N700 were affected by semantic priming and by face-name learning and identification. The early fraction of N700 and face-specific P350 exhibited significant habituation. About half of the AP350 sites exhibited semantic priming, whereas the VP350 and LP350 sites did not. Cortical stimulation evoked a transient inability to name familiar faces or evoked face-related hallucinations at two-thirds of face-specific N200 sites. These results are discussed in relation to human behavioral studies and monkey single-cell recordings. Discussion of results of all three papers concludes that: face-specific N200 reflects the operation of a module specialized for the perception of human faces; ventral and lateral occipitotemporal cortex are composed of a complex mosaic of functionally discrete patches of cortex of variable number, size and location; in ventral cortex there is a posterior-to-anterior trend in the location of patches in the order letter-strings, form, hands, objects, faces and face parts; P290 and N700 at face-specific N200 sites, and face-specific P350, are subject to top-down influences.

Comparative localization of auditory comprehension by using functional magnetic resonance imaging and cortical stimulation

Abstract: Object. The authors previously described a functional magnetic resonance (fMR) imaging task for the localization of auditory comprehension in which focal activation of posterior temporal and inferior frontal regions of the left hemisphere was reliably demonstrated. Because this study was conducted in neurologically normal volunteers, it was not possible to determine whether the activated regions were critical to the performance of language tasks; that is, whether the fMR imaging activations provided a valid measure of language processing. A direct comparison of fMR imaging language activation with cortical stimulation must be completed before it can be used with confidence in presurgical planning, and this comparison is performed in the present study. Methods. The authors report on a series of 33 consecutive patients who underwent dominant hemisphere resection and in whom fMR imaging mapping of auditory comprehension was performed at the Yale neurosurgical program. In 23 of the 33 patients fMR imaging act...

Functional magnetic resonance imaging identifies abnormal visual cortical function in patients with occipital lobe epilepsy.

Abstract: Summary: Purpose: To determine whether functional magnetic resonance imaging (fMRI) can reliably identify lateralized cortical dysfunction in patients with suspected occipital lobe epilepsy. Methods: We compared visual cortical function of 10 patients with intractable occipital lobe epilepsy with nine control subjects' fMRI. Visual stimulation by using an alternating checkerboard pattern results in transient increases in the intensity of the proton magnetic resonance signal of water in the occipital lobes during echo-planar imaging. We used these stimulus-dependent changes in signal intensity to construct functional activation maps, which we registered onto anatomic images. Results: After full-field stimulation, none of the patients with occipital lobe epilepsy had normal activation patterns, whereas eight of the nine control subjects had normal patterns (p = 0.001). Abnormalities consisted of either a markedly asymmetric activation pattern in six of 10 patients (p = 0.04), or a complete absence of activation in four of 10 patients (p = 0.05). The abnormal side of activation was concordant with the side of seizure onset in all six patients with asymmetric activation maps. Half-field stimulation produced less reliable results. Although more patients had abnormal activation maps than did controls with half-field stimulation (p = 0.04), the abnormal side was discordant with the side of seizure onset in three of the five patients who had markedly asymmetric activation patterns. Conclusions: These results suggest that fMRI with full-field stimulation is a reliable, noninvasive method for identifying areas of abnormal visual cortical function ipsilateral to the epileptogenic region in patients with occipital lobe epilepsy.

Event-related potentials and functional MRI: a comparison of localization in sensory, perceptual and cognitive tasks.

Abstract: Combining ERP and fMRI methods to elucidate the time course and anatomical basis of information processing may provide a powerful new tool for understanding human brain function. Attempts to model the time course of fMRI activations by recording surface electromagnetic fields require a better understanding of the relationship between ERPs and fMRI activations. The results presented here show that good correspondence can be obtained between the location of ERP generators and fMRI activations in sensorimotor cortex, and in face perception and target detection tasks. However, difficulties in obtaining somatosensory fMRI activations with stimuli known to evoke robust SEPs, and the lack of fMRI activations within the hippocampus in tasks that elicit large hippocampal field potentials suggest that not all stimuli or tasks that evoke focal ERPs will evoke fMRI activations. This may be related to differences in the sensitivity of the fMRI that will be overcome with better technique and with more sensitive instruments. However, caution must be exercised in developing models that assume a one-to-one correspondence between ERP generators and fMRI activations.