Biomedical subjects
Publications and source records attributed to A Puce.
We have studied the scalp and intracerebral recordings of 12 patients with intractable temporal lobe epilepsy. The intracerebral P300 provides useful diagnostic information regarding the epileptogenicity of a temporal lobe. The scalp P300, by nature of its bilateral scalp distribution, is unable to be used diagnostically in assessing candidates for possible anterior temporal lobectomy.
We studied the effects of age on the limbic and scalp P3 in 45 patients with intracranial electrodes implanted for pre-surgical investigation of focal seizures. Scalp P3 data from a reference group of 24 healthy control subjects were also analyzed for comparison. An auditory oddball paradigm with infrequent stimuli being presented with a probability of 0.20 was used. In normals P3 latency increased by 1.34 msec/year (r = 0.60, P less than 0.01). In the patients limbic and scalp P3 latency increased linearly as a function of increasing age at a rates of 3.85 msec/year (r = 0.58, P less than 0.001) and 2.71 msec/year (r = 0.56, P less than 0.01), respectively. The rate of increase of P3 latency with age was significantly lower in the normal controls, as compared to both the patient scalp (t = 1.79, P less than 0.05) and depth (t = 2.25, P less than 0.005) ERP data. There was no significant difference between the slopes of the patient P3 latency versus age scalp and depth data (t = 1.09, P greater than 0.1). Unlike for normal controls, there was no relationship between age and limbic P3 amplitude (r = 0.02, P greater than 0.1) or age and scalp P3 amplitude (r = 0.17, P greater than 0.1). The differences between controls and patients could be due to: (i) effects of chronic seizures; (ii) long-term effects of anticonvulsant use; (iii) the use of a relatively long inter-stimulus interval which may have selectively affected the patients.(ABSTRACT TRUNCATED AT 250 WORDS)
Electrophysiological correlates of the processing of visual information were studied in epileptic patients with electrodes chronically implanted on the surface of striate and extrastriate cortex. In separate experiments patients viewed faces, letter strings (words and non-words), numbers, and control stimuli. A negative potential, N200, was evoked by faces, letter strings, and numbers, but not by the control stimuli. N200 was recorded bilaterally from discrete regions of the fusiform and inferior temporal gyri. These category-specific face, letter-string, and number "modules" vary in location. In most cases there was no overlap in the location of face and letter-string modules, suggesting a mosaic of functionally discrete regions. In some cases letter-string and number N200s were recorded from the same location, suggesting that these modules may be less spatially and functionally discrete. Face N200-like potentials can be recorded from temporal scalp, allowing the possibility of studying early face processing in normal subjects. Longer-latency face-specific potentials were recorded from the inferior surface of the anterior temporal lobe. Potentials evoked by colored checkerboards were recorded from a region of the fusiform gyrus posterior to the fusiform region from which category-specific N200s were recorded. These results suggest that there are several processing streams in inferior extrastriate cortex. In addition to object recognition systems previously proposed for faces and words, our preliminary results suggest a separate system dealing with numbers. Postulated systems dealing with larger manipulable objects and animals have not been detected.
Separate working memory domains for spatial location, and for objects, faces, and patterns, have been identified in the prefrontal cortex (PFC) of nonhuman primates. We have used functional magnetic resonance imaging to examine whether spatial and nonspatial visual working memory processes are similarly dissociable in human PFC. Subjects performed tasks which required them to remember either the location or shape of successive visual stimuli. We found that the mnemonic component of the working memory tasks affected the hemispheric pattern of PFC activation. The spatial (LOCATION) working memory task preferentially activated the middle frontal gyrus (MFG) in the right hemisphere, while the nonspatial (SHAPE) working memory task activated the MFG in both hemispheres. Furthermore, the area of activation in the left hemisphere extended into the inferior frontal gyrus for nonspatial SHAPE task. A perceptual target (DOT) detection task also activated the MFG bilaterally, but at a level approximately half that of the working memory tasks. The activation in the MFG occurred within 3-6 s of task onset and declined following task offset. Time-course analysis revealed a different pattern for cingulate gyrus, in which activation occurred upon task completion. Cingulate gyrus activation was greatest following the SHAPE task and was greater in the left hemisphere. The present results support the prominent role of the PFC and, specifically, the MFG in working memory, and indicate that the mnemonic content of the task affects the relative weighting of hemispheric activation.
Auditory oddball scalp and limbic P3s were recorded from 18 patients with unilateral temporal lobe epilepsy (TLE) prior to seizure surgery. Limbic P3s were unilaterally absent ipsilateral to the seizure focus and were present in the nonepileptogenic temporal lobe in all 18 cases studied. Scalp P3s, recorded from C3 and C4, on the other hand, were elicited bilaterally and there was no significant difference in amplitude or latency between the epileptogenic and nonepileptogenic sides. These data concur with studies of scalp P3 performed following surgery and suggest that the assessment of the contribution of limbic P3 to scalp P3 may be masked by volume conduction effects and other generators of P3. We conclude that the P3 recorded from central scalp sites, unlike its limbic counterpart, offers little clinical information in the presurgical assessment of patients with TLE.