Potent antitumor activity of MS-247, a novel DNA minor groove binder, evaluated by an in vitro and in vivo human cancer cell line panel.

We synthesized a novel anticancer agent MS-247 (2-[[N-[1-methyl-2-[5-[N-[4-[N,N-bis(2-chloroethyl) amino] phenyl]] carbamoyl]-1H-benzimidazol-2-yl] pyrrol-4-yl] carbamoyl] ethyldimethylsulfonium di-p-toluenesulfonate) that has a netropsin-like moiety and an alkylating residue in the structure. We evaluated antitumor activity of MS-247 using a human cancer cell line panel coupled with a drug sensitivity database and subsequently using human cancer xenografts. The average MS-247 concentration required for 50% growth inhibition against a panel of 39 cell lines was 0.71 microM. The COMPARE analysis revealed that the differential growth inhibition pattern of MS-247 significantly correlated with those of camptothecin analogues and anthracyclins, indicating that MS-247 and the two drug groups might have similar modes of action. MS-247 exhibited remarkable antitumor activity against various xenografts. A single i.v. injection of MS-247 significantly inhibited the growth of all 17 xenografts tested, which included lung, colon, stomach, breast, and ovarian cancers. In many cases, MS-247 was more efficacious than cisplatin, Adriamycin, 5-fluorouracil, cyclophosphamide, VP-16, and vincristine and was almost comparable with paclitaxel and CPT-11; these are the most clinically promising drugs at present. MS-247 was noticeably more effective than paclitaxel (in HCT-15) and CPT-11 (in A549, HBC-4, and SK-OV-3). The toxicity of MS-247, indicated by body weight loss, was reversible within 10 days after administration. The MS-247 mode of action showed DNA binding activity at the site where Hoechst 33342 bound, inhibited topoisomerases I and II (as expected by the COMPARE analysis) blocked the cell cycle at the G2-M phase, and induced apoptosis. These results indicate that MS-247 is a promising new anticancer drug candidate to be developed further toward clinical trials.

Kinetic study of the reaction of vitamin C with vitamin E radicals (tocopheroxyls) in solution.

New stable vitamin E radicals (7-tert-butyl-5-isopropyltocopheroxyl (4), 5,7-diisopropyltocopheroxyl (5), 7-tert-butyl-5-methyltocopheroxyl (6), and 5,7-diethyltocopheroxyl (7] with two bulky alkyl substituents at ortho positions (C-5 and C-7) have been prepared, and the reaction rates of vitamin C (ascorbic acid (1) and 6-O-stearyl ascorbic acid (2] with these tocopheroxyl radicals in benzene/ethanol/water (2:1:0.1, v/v) solution have been determined spectrophotometrically, using a stopped-flow technique. The second-order rate constants, k2, obtained vary in the order of 10(3), and decrease dramatically in the order 7 greater than 6 greater than 5 greater than 4, as the size of two ortho-alkyl groups in tocopheroxyl increases. The result suggests that the effect of steric hindrance on the reaction rate is considerable. These reaction rates were compared with those of vitamin C with alpha-tocopheroxyl reported by Packer et al. (Nature 278 (1979) 737-738) and Scarpa et al. (Biochim. Biophys. Acta 801 (1984) 215-219).

High-speed video analysis of acoustically oscillated guinea pig stapes.

OBJECTIVE: We investigated the ossicular movement in the near-intact middle ear in response to acoustic stimulation using a high-speed video camera and video analysis software program. DESIGN: We have designed a good visual access to the middle ear of the guinea pig by opening the ventral wall of the otic capsule, without injuring the sound-conducting structures, from the external auditory canal to the oval window. The high-speed video camera could record analysable ossicular motion up to 4000 frames per second. RESULTS: The stapes showed reciprocal movement in the same frequency as the stimulating tone, and with an amplitude proportional to the stimulating sound intensity. Injury to the tympanic membrane attenuated the stapedial motion, which was recovered to that of the control level by patch repair of the perforation. CONCLUSION: Our experimental set-up was capable of evaluating the conductive hearing, regardless of the status of the animal's sensorineural hearing or even life. Such a video analysis may provide a powerful tool to investigate the physiology of the middle ear.

Decrease in cortical benzodiazepine receptors in symptomatic patients with leukoaraiosis: a positron emission tomography study.

BACKGROUND AND PURPOSE: [11C]flumazenil (FMZ), a ligand that selectively binds to the central benzodiazepine receptor in the neuronal membrane, is useful for evaluating neuronal viability in a positron emission tomography (PET) scan. Using this ligand, we investigated whether there was a correlation between neuronal integrity in various brain structures and dementia in patients with leukoaraiosis. METHODS: Twelve patients with extensive leukoaraiosis on magnetic resonance imaging were divided into groups of patients with or without dementia. Based on a 2-compartment, 2-parameter model that included metabolite-corrected arterial input and PET-measured cerebral radioactivity, the distribution volume of FMZ (FMZ-V(d)) was calculated in various regions of interest by nonlinear curve fitting. Additionally, tracer kinetic analysis was applied for voxel-by-voxel quantification of FMZ-V(d), and data analysis was performed by statistical parametric mapping. RESULTS: The presence of dementia was associated with a reduced FMZ-V(d) in widespread areas of the cerebral cortex, including the bilateral frontopolar and frontal/insular areas, the left temporo-occipital border areas, and the left marginal cortical areas. CONCLUSIONS: Differences in neuronal integrity in the cerebral cortex might determine whether patients with leukoaraiosis become symptomatic or not.

Effects of hyperglycemia on FDG uptake in human brain and glioma.

UNLABELLED: This study evaluates the effects of hyperglycemia on fluorodeoxyglucose (FDG) uptake in the human brain and in brain tumors. METHODS: We performed glucose loading during FDG PET studies in nine patients with brain tumors (eight gliomas and one brain metastasis) and one with resected glioma. Two FDG PET scans were obtained in all cases within 1 wk in a control state and with glucose loading by intravenous infusion of 10% glucose solution. Serial arterial blood sampling was performed in all cases to obtain fractional uptake of FDG normalized by the plasma integral uptake of radioactivity (FU). RESULTS: In all nine patients with brain tumors, the tumor was depicted more clearly with glucose loading than in the control state. Glucose loading decreased FU in the cerebral cortex (54.2% +/- 13.8%) nearly in inverse proportion to the plasma glucose level, while the tumors showed a decrease (42.5% +/- 15.6%), resulting in an increased tumor-to-cortex ratio by 26.0% +/- 5.7%. Fractional uptake in the cerebellum, white matter and the edematous area also decreased by glucose loading (53.9% +/- 13.2%, 49.6% +/- 10.3% and 34.9% +/- 9.6%, respectively). CONCLUSION: These results demonstrate the different effects of hyperglycemia on normal brain tissue and on tumor, suggesting that glucose loading may be a valuable adjunct to FDG PET to enhance detection of recurrent or residual brain tumors.

Clinical application and quantitative evaluation of generator-produced copper-62-PTSM as a brain perfusion tracer for PET.

UNLABELLED: Copper-62-pyruvaldehyde bis(N4-methylthiosemicarbazone) copper II (62Cu-PTSM) has been proposed as a generator-produced positron-emitting tracer for perfusion imaging. To evaluate the characteristics of 62Cu-PTSM as a cerebral perfusion tracer, brain PET images of 62Cu-PTSM were compared with cerebral blood flow (CBF). METHODS: Following an intravenous injection of 62Cu-PTSM, a serial dynamic PET scan was performed for 10 min with arterial sampling in 10 subjects. CBF was measured by 15O-labeled water before the 62Cu-PTSM study. RESULTS: Dynamic PET scan with octanol-extracted arterial input function indicated the presence of significant back-diffusion of 62Cu-PTSM from the brain within 3 min after injection, followed by stable activity from 3 to 10 min. Comparison with 15O-water PET demonstrated less contrast between high- and low-flow regions in 62Cu-PTSM image and a nonlinear relationship of flow and 62Cu-PTSM uptake, which suggests the underestimation of CBF in high-flow regions due to the existence of back-diffusion. CONCLUSION: Although 62Cu-PTSM can be used widely for evaluation of brain perfusion with PET, kinetic analysis and correction may be needed to quantify regional CBF.

Quantification of regional cerebral blood flow with continuous infusion of technetium-99m-ethyl cysteinate dimer.

UNLABELLED: We propose a new method to quantify regional cerebral blood flow (rCBF) with continuous infusion of 99mTc-ethyl cysteinate dimer (ECD) and dynamic SPECT. METHODS: Thirteen subjects were studied. Seven subjects had SPECT and PET studies, and the other six subjects were involved in the measurement of blood clearance of 99mTc-ECD. During constant infusion of 99mTc-ECD (740 MBq) over 10 min, dynamic SPECT scans were obtained every 1 min by means of a triple-head rotating SPECT camera. Intermittent arterial blood sampling with octanol extraction was performed every 1 min to estimate the arterial input function. Influx constant (Ku) obtained by Gjedde-Patlak graphical plot method was compared with rCBF measured by PET using 15O CO2 steady state method. In order to simplify the procedure, arterial input function in each subject was estimated by calibration of the arterial blood sampled at the end of the scan to the standard arterial input function estimated from the blood clearance rate in six subjects. RESULTS: Ku was linearly correlated with rCBF (Ku = 0.09 + 0.62 rCBF, r = 0.85, p < 0.05). Ku calculated with the estimated input function (Ku') and rCBF also demonstrated a linear relationship (Ku' = 0.05 + 0.65 rCBF, r = 0.84, p < 0.05). CONCLUSION: The proposed method with one-point arterial sampling is a simple, clinically feasible tool for quantitative measurement of rCBF with 99mTc-ECD.

One-day protocol for cerebral perfusion reserve with acetazolamide.

UNLABELLED: A one-day protocol with a double injection of 99mTc-ECD was introduced for the assessment of cerebral perfusion reserve with acetazolamide (ACZ). The purpose of this study was to investigate the feasibility and effectiveness of this protocol. METHODS: Thirty subjects were given double injections of 99mTc-ECD (first dose 370 MBq; second dose 740 MBq) for consecutive brain perfusion studies. Serial dynamic SPECT scans (1 min x 50 frames) were performed with the first set of SPECT data obtained by totaling the data for the frames taken between 5 and 20 min, and the second by subtracting the decay and dose-corrected initial SPECT data from the sum of the data obtained between 35 and 50 min. To evaluate the feasibility and effectiveness of the procedure, 23 of the 30 subjects were injected with ACZ 14 min after the first dose. To evaluate the reproducibility, seven subjects were not given the ACZ. The washout rate (WR) was calculated for three stages (WR1 = from 6 to 14 min, WR2 = from 20 to 28 min, and WR3 = from 36 to 44 min). Regional count increase (percent increase) and the percent count difference between normal and affected side (percent difference) were also calculated. RESULTS: Values for WR1, WR2 and WR3 did not show significant differences among the stages (WR1 = -1.43% +/- 6.09%, WR2 = -0.65% +/- 6.57%, and WR3 = -1.60% +/- 4.28%; F-value = 0.33, p-value = 0.72). Reproducibility was excellent (second SPECT = 0.964 x first SPECT; r = 0.997). Mean count increase after ACZ was 21.7%. In patients with unilateral cerebrovascular disease, the percent increase after ACZ loading was significantly greater on the normal side (26.6% +/- 13.0%) than on the affected side (19.3% +/- 13.2%) (p < 0.01), resulting in a significant increase in percent difference (control: 14.3% +/- 10.7%, ACZ: 19.2% +/- 11.5%; p < 0.01). CONCLUSION: ECD washout was minimal during the first 50 min after injection and was not affected by ACZ, which supports the feasibility of this protocol. The simple procedure and short acquisition time of this method renders it clinically useful for measuring cerebral perfusion reserve.

Measurement of regional cerebral plasma pool and hematocrit with copper-62-labeled HSA-DTS.

UNLABELLED: We developed copper-62-labeled human serum albumin-dithiosemicarbazone (62Cu-HSA-DTS) as a blood-pool imaging agent for PET. To evaluate 62Cu-HSA-DTS for plasma-pool imaging and to measure the regional cerebral hematocrit, 12 normal volunteers and 7 patients with cerebrovascular disease underwent PET studies with 62Cu-HSA-DTS and 15O-labeled carbon monoxide (C15O). METHODS: The normal subjects were studied with both C15O and 62Cu-HSA-DTS. All patients were examined by 15O-gas studies to measure cerebral perfusion and oxygen metabolism, followed by measurement of plasma volume with 62Cu-HSA-DTS for analysis of regional cerebral hematocrit. Regional cerebral hematocrit was calculated from regional cerebral red cell volume (rCRCV) measured by C15O and regional plasma volume (rCPV) measured by 62Cu-HSA-DTS in each subject, and the regional cerebral/large-vessel hematocrit ratio was obtained for both cerebral hemispheres in each subject. RESULTS: Mean regional cerebral hematocrit and mean cerebral/large-vessel hematocrit ratio in the 12 normal volunteers were 38.3 +/- 3.45% and 0.88 +/- 0.06, respectively. In the seven patients with cerebrovascular disease, regional cerebral hematocrit was significantly lower on the hypoperfused side than the normal hemisphere. The images of rCPV and rCRCV from these patients demonstrated a greater increase in rCPV than rCRCV in the hypoperfused area. CONCLUSION: These results suggest that 62Cu-HSA-DTS can be used for measurement of plasma volume and that regional cerebral hematocrit may provide valuable information regarding the microcirculation in the brain.

Measurement of regional cerebral blood flow with copper-62-PTSM and a three-compartment model.

UNLABELLED: We evaluated quantitatively 62Cu-labeled pyruvaldehyde bis(N4-methylthiosemicarbazone) copper II (62Cu-PTSM) as a brain perfusion tracer for positron emission tomography (PET). For quantitative measurement, the octanol extraction method is needed to correct for arterial radioactivity in estimating the lipophilic input function, but the procedure is not practical for clinical studies. To measure regional cerebral blood flow (rCBF) by 62Cu-PTSM with simple arterial blood sampling, a standard curve of the octanol extraction ratio and a three-compartment model were applied. METHODS: We performed both 15O-labeled water PET and 62 Cu-PTSM PET with dynamic data acquisition and arterial sampling in six subjects. Data obtained in 10 subjects studied previously were used for the standard octanol extraction curve. Arterial activity was measured and corrected to obtain the true input function using the standard curve. RESULTS: Graphical analysis (Gjedde-Patlak plot) with the data for each subject fitted by a straight regression line suggested that 62Cu-PTSM can be analyzed by the three-compartment model with negligible K4. Using this model, K1-K3 were estimated from curve fitting of the cerebral time-activity curve and the corrected input function. The fractional uptake of 62Cu-PTSM was corrected to rCBF with the individual extraction at steady state calculated from K1-K3. The influx rates (Ki) obtained from three-compartment model and graphical analyses were compared for the validation of the model. A comparison of rCBF values obtained from 62Cu-PTSM and 150-water studies demonstrated excellent correlation. CONCLUSION: The results suggest the potential feasibility of quantitation of cerebral perfusion with 62Cu-PTSM accompanied by dynamic PET and simple arterial sampling.

Extraction and retention of technetium-99m-ECD in human brain: dynamic SPECT and oxygen-15-water PET studies.

UNLABELLED: The kinetic behavior of 99mTc-ethyl cysteinate dimer (99mTc-ECD) in the human brain was investigated in six normal volunteers. METHODS: Dynamic SPECT and a three-compartmental model were used to estimate the rate constants of 99mTc-ECD in normal human brain. Extraction fraction (E), retention fraction (R) and permeability surface area product (PS product) of 99mTc-ECD were calculated using the rate constants. Regional cerebral blood flow (rCBF) was measured by PET with 15O-water. RESULTS: The rate constants in the cerebral cortex were estimated as 0.307 +/- 0.021 for K1 (influx constant), 0.201 +/- 0.047 for k2 (backdiffusion rate constant), 0.547 +/- 0.103 for k3 (lipophilic-to-hydrophilic conversion constant) and 0.0028 +/- 0.0012 for k5 (rate constant from lipophilic compartment to blood) at rCBF of 0.509 +/- 0.055 ml/g/min (mean +/- s.d.). The first-pass extraction, retention fraction and PS product were calculated as 0.608 +/- 0.069, 0.734 +/- 0.047 and 0.477 +/- 0.060, respectively. The first-pass extraction of 99mTc-ECD decreased significantly with increases in rCBF. The retention fraction and PS product of 99mTc-ECD did not show significant changes within the normal range of rCBF. The net extraction of 99mTc-ECD calculated from the static SPECT image obtained from 20 to 40 min was 0.358 +/- 0.039 in the cortex. CONCLUSION: Technetium-99m-ECD has a fairly high brain extraction, and its retention fraction and PS product appear to be independent of rCBF in the healthy human brain.

Noninvasive quantification of iodine-123-iomazenil SPECT.

UNLABELLED: The feasibility of a noninvasive method for quantification of [123I]iomazenil binding using a standardized arterial input function and a single venous blood sample was assessed in normal volunteers. METHODS: Serial SPECT images and blood data from six healthy male volunteers after intravenous injection of [123I]iomazenil were used. The standardized input function was derived by averaging the six subjects' arterial curves. Individual input functions were estimated by calibrating the standardized input function with one-point venous blood radioactivity concentration. Ligand transport (K1) and receptor binding were computed from the estimated input functions and two separate SPECT scans using a table look-up procedure based on a three-compartment, two-parameter model. Reference values for K1 and receptor binding were determined from the serial SPECT data and individual arterial curves using a three-compartment, three-parameter model and curve fitting. RESULTS: Analyses of the error caused by the calibration in relation to the time postinjection revealed that the optimal calibration time was 30 min postinjection. Receptor binding obtained by this simplified method correlated well with the reference values (r = 0.941) and was estimated within an error of 10% in the cerebral cortical regions. Although the estimated K1 showed relatively poor correlation (r = 0.699) with the reference value, it was an excellent relative measure in each subject. CONCLUSION: Our method provided an absolute measure of the benzodiazepine receptor binding and a relative measure of ligand transport from two SPECT scans and a venous blood sample. This method would be useful for quantitative assessment of benzodiazepine receptors in clinical settings.

Simple quantification of benzodiazepine receptor binding and ligand transport using iodine-123-iomazenil and two SPECT scans.

UNLABELLED: The feasibility of simplified procedures for the quantification of benzodiazepine receptor binding using [123I]iomazenil and SPECT was assessed. METHODS: Six normal male volunteers were studied. Following intravenous injection of 111 MBq [123I]iomazenil, serial dynamic SPECT scanning was performed for 120 min and the concentration of lipophilic compounds in the arterial plasma was determined by chloroform extraction. Kinetic parameters were estimated by a curve-fitting procedure using the following four models: three-compartment, four-parameter (K1-k4) (3C4P), three-compartment, three-parameter (fixed K1/k2) (3C3P), three-compartment, two-parameter (fixed K1/k2 and k4) (3C2P) and two-compartment, two-parameter (K1 and k2) (2C2P). Kinetic parameters were also calculated by a table look-up procedure with 3C2P using only two SPECT data acquisitions. Parametric images were generated based on the same procedure. RESULTS: In all models, the curve-fitting procedure gave similar outcomes for ligand transport (K1) and receptor density parameters (i.e., binding potential or distribution volume). The 3C4P parameters showed significant correlation between k2 and k3, while 3C3P did not show such a correlation, suggesting the stability of 3C3P. The 3C2P provided parameters essentially identical to those with the 3C3P, indicating the suitability of this model, while 2C2P gave similar distribution volume but obviously low K1. CONCLUSION: Table look-up procedures based on the 3C2P model permit quantification of benzodiazepine receptor binding using [123I]iomazenil with two SPECT scans. This method may be of clinical value in the diagnosis of various diseases.

Evaluation of a double-injection method for sequential measurement of cerebral blood flow with iodine-123-iodoamphetamine.

UNLABELLED: To test the feasibility of applying N-isopropyl-[123I]p-iodoamphetamine (IMP) for sequential measurements of regional cerebral blood flow (rCBF) with injection of two separate doses in a single procedure, kinetic analysis based on a two-compartment model was done using dynamic SPECT data. A microsphere model analysis without consideration of IMP washout from the brain was also tested for clinical application. METHODS: A dynamic SPECT scan consisting of fifty 1-min scans was obtained on 15 patients using a three-head rotating gamma camera with two separate doses of IMP (111 MBq each) at the beginning and 25 min after scan initiation. The reproducibility of two resting rCBF scans was tested in six patients and the cerebrovascular response shown by increased rCBF with acetazolamide (1 g) was assessed in nine patients. RESULTS: Two-compartment model analysis showed excellent reproducibility of resting rCBF scans and significantly different cerebrovascular reactivity to acetazolamide between areas with and without ischemia. Microsphere model analysis showed smaller values in the first rCBF image by 3% and in the second by 10%, resulting in lower values for cerebrovascular reactivity. The difference in cerebrovascular reactivity between ischemic and nonischemic areas, however, is highly significant. CONCLUSION: The double-injection method for IMP is feasible for two sequential rCBF measurements in a single procedure and is applicable for acetazolamide challenge. Simple microsphere model analysis, as well as a two-compartment model analysis, provide reliable assessment for cerebrovascular reactivity despite the complex dynamics of IMP and are feasible for clinical application.

Delayed data acquisition for optimal PET activation studies with oxygen-15-water in cerebral arteriovenous malformation.

UNLABELLED: In the clinical application of activation PET studies with 15O-water, optimal PET images are required when the high activity of a nearby lesion might affect the activated area. METHODS: To determine the optimal time for data acquisition of PET images, we performed serial dynamic PET measurements in five patients with cerebral arteriovenous malformation (AVM). All AVMs were closest to the motor cortices, and the activation task was opponent finger movement contralateral to the AVM. Activation PET and MR images were coregisterated for localization of activated foci. RESULTS: Time-activity curves of the nidus and normal cortex from the dynamic PET data demonstrated a discrepancy in peak time and significant radioactivity increase in the nidus during the early phase. Elimination of the initial PET data provided better contrast in activated foci without affecting the calculated cerebral blood flow of other areas. CONCLUSION: Delayed data acquisition can avoid interference of the AVM nidus with the activated area.

Ultra-high resolution SPECT system using four pinhole collimators for small animal studies.

UNLABELLED: We describe a newly developed ultra-high resolution SPECT system using four pinhole collimators for small animal studies. METHODS: The system utilizes a clinical four-head SPECT scanner with specially designed pinhole collimators. Four types of pinholes with different configurations were designed with different effective aperture sizes (1.0, 2.0 and 4.0 mm) and rotating radii (40 mm and 50 mm). The distance from the axis of rotation to the scintillator was fixed to 180 mm. A filtered backprojection algorithm was used to reconstruct SPECT images after fanbeam-to-parallel-beam data conversion. RESULTS: The system provided a reconstructed spatial resolution of 1.65 mm (FWHM) and sensitivity of 4.3 kcps/microCi/ml with the best type of pinholes, respectively. The 99mTc-HMPAO SPECT image in rat studies clearly visualized small brain structures, and the left ventricular myocardium and cardiac cavity were clearly separated with 99mTc-MIBI. Dynamic SPECT imaging of rat brain with [123I]iomazenil was also feasible. CONCLUSION: This ultra-high resolution SPECT system can be used to measure the regional distribution of radiolabeled tracers in small animals in vivo and may play a significant role in the development of new radiopharmaceuticals and in studies of various disease models using living animals.

Studies on the activation mechanism of fibrinolytic enzyme system in plasma by human pancreatic elastase.

In the present study, the activation mechanism of fibrinolytic enzyme system in plasma by human pancreatic elastase was investigated. It was confirmed that human pancreatic elastase not only converted the co-existing plasminogen to low molecular weight-plasminogen which could be easily activated by the activator, but also inhibited alpha 2-macroglobulin and alpha 2-plasmin inhibitor which are antiactivators or fast reacting antiplasmins, and consequently, induced the activation of the fibrinolytic enzyme system in plasma.

Cortical activation with sound stimulation in cochlear implant users demonstrated by positron emission tomography.

Six postlingually deaf patients using multi-channel cochlear implants were examined by positron emission tomography (PET) using 15O-labeled water. Changes in regional cerebral blood flow (rCBF) were measured during different sound stimuli. The stimulation paradigms employed consisted of two sets of three different conditions; (1) no sound stimulation with the speech processor of the cochlear implant system switched off, (2) hearing white noise and (3) hearing sequential Japanese sentences. In the primary auditory area, the mean rCBF increase during noise stimulation was significantly greater on the side contralateral to the implant than on the ipsilateral side. Speech stimulation caused significantly greater rCBF increase compared with noise stimulation in the left immediate auditory association area (P < 0.01), the bilateral auditory association areas (P < 0.01), the posterior part of the bilateral inferior frontal gyri; the Broca's area (P < 0.01) and its right hemisphere homologue (P < 0.05). Activation of cortices related to verbal and non-verbal sound recognition was clearly demonstrated in the current subjects probably because complete silence was attained in the control condition.

Cortical processing mechanism for vocalization with auditory verbal feedback.

To investigate the relationship between motor and sensory speech center, cortical activity was examined using PET while normal subjects perceived their own voice which sounded different to the articulated one. The results showed significant activation in the superior temporal gyri with absence of activity in the supplementary motor area (SMA). In a previous study we found significant activation in SMA with no activity in the superior temporal gyrus when normal subjects simply vocalized. Thus, two different cortical pathways for vocalization were delineated: programmed pathway in SMA, and pathway with auditory verbal feedback. The former is thought to be the mature system in the adult, and the latter may be related to speech acquisition.

The role of the temporal coding system in the auditory cortex on speech recognition.

To elucidate the temporal coding system for speech recognition, we synthesized stimulation sounds which do not contain formant information but do contain temporal information by transforming original sound wave to click sequences. Using this stimulation sound, we performed a recognition test and used PET to examine the cortical activities in normal subjects listening to this sound. The results of the recognition test showed a good perception of the sounds made from sequential speech. The PET study demonstrated significant activation of the superior temporal gyri while listening to the stimulation speech sounds. Our results imply that these stimulation sounds were processed semantically in the auditory cortices. The temporal processing system is thought to make an important contribution to speech recognition.