Biomedical subjects
Norman Tepley
Publications and source records attributed to Norman Tepley.
Language laterality determined by MEG mapping with MR-FOCUSS.
Magnetoencephalography recordings were made on 27 patients with localization related epilepsy during two different language tasks involving semantic and phonological processing (verb generation and picture naming). These patients underwent the semi-invasive intracarotid amobarbital procedure (IAP), also referred to as the Wada test, to determine the language-dominant hemisphere. Magnetoencephalography (MEG) data were analyzed by MR-FOCUSS, a current density imaging technique. A laterality index (LI) was calculated from this solution to determine which hemisphere had more neural activation during these language tasks. The LIs for three separate latencies, within each language task, were calculated to determine the latency that correlated best with each patient's IAP result. The LI for all language processing was calculated for the interval 150-550 ms, the second LI was calculated for the interval 230-290 ms (Wernicke's activation), and the third LI was calculated for the interval 396-460 ms (Broca's activation). In 23 of 24 epilepsy patients with a successful IAP, the LIs for Broca's activation, during the picture naming task, were in agreement with the results of the IAP (96% agreement). One of three patients who had an undetermined or bilateral IAP had an LI calculated for Broca's activation (396-460 ms) that agreed with intracranial mapping and clinical testing. These results indicate an 89% agreement rate (24 of 27) for magnetoencephalographic LI determination of the hemisphere of language dominance.
Magnetoencephalographic localization of the basal temporal language area.
Magnetoencephalography (MEG) recordings were made on 25 native English-speaking patients with localization-related epilepsy during a semantic language task (verb generation). Eighteen right-handed subjects with normal reading ability had MEG scans performed during the same language task. MEG data was analyzed by MR-FOCUSS, a current density imaging technique. Detectable MEG signals arising from activation in the left fusiform gyrus, also known as the basal temporal language area (BTLA), occurred at 167 +/- 18 ms (n = 43) in all subjects. The BTLA has been associated with a variety of language production and comprehension tasks involving processing of semantic, orthographic, and phonologic information. MEG may become an important tool in efforts to further define the linguistic operations of specific regions within this language area.
Magnetoencephalographic validation parameters for clinical evaluation of interictal epileptic activity.
The authors demonstrate that the confidence volume (the spatial volume that encompasses the 95% probability of source localization) of the single equivalent current dipole is helpful in validating magnetoencephalographic epileptic spike mapping. Such mapping involves distinguishing spikes from other neuronal events. The usual criteria for validating dipole fit reliability involve four parameters-correlation coefficient (R > or =0.98), goodness of fit (> or =0.95), root mean square magnetic field value (>400 fT), and dipole moment (Q value > 200 nAm)-but other parameters (direction of dipole moment, location of dipole, and confidence volume) can be considered. In 21 patients with epilepsy, the average correlation coefficient for 608 epileptic spikes was 0.99; average goodness of fit, 0.98; average root mean square, 1,198 fT; and the average Q value, 370 nAm. The mean average confidence volume was 0.30 +/- 0.27 cm3. Correlation coefficient values for quiet brain activity were less than 0.90; goodness of fit values, less than 0.85; and confidence volumes were large (>5 cm3); and for noise runs (no subject) they were even larger (>100 cm3), although correlation coefficient values were more than 0.80 and goodness of fit values were more than 0.85. Confidence volumes for noise data are large-for background brain activity even larger-but confidence volumes for epileptic spikes are small. Confidence volume, in conjunction with other parameters, may be a robust parameter for spike selection.
Cortical hyperexcitability in migraine patients before and after sodium valproate treatment.
DC-magnetoencephalography (DC-MEG)waveforms arising during migraine aura were used to determine the effectiveness of prophylactic medication therapy on neuronal hyperexcitability. Nine patients were prescribed valproate (Depakote) for migraine prophylaxis. MEG scans were recorded during visual stimulation before commencing medication and again after 30 days of daily use of valproate. Cortical brain activity was recorded during stimulation with a black-and-white circular checkerboard pattern alternating at 8 Hz and were analyzed with MR-FOCUSS. Large-amplitude DC-MEG signals, imaged to extended areas of occipital cortex, were seen before therapy. After 30 days of prophylactic treatment, reduced DC-MEG shifts in the occipital cortex and reduced incidence of migraine attacks were observed. Using visual stimulation, the authors demonstrated the hyperexcitability of widespread regions throughout occipital cortex in migraine patients, explaining the susceptibility for triggering spreading cortical depression and migraine aura. This study confirms that MEG can noninvasively determine the status of neuronal excitability before and after therapy. This finding may be helpful in determining which prophylactic medications will be most effective in reducing hyperexcitability in particular patients.