Dendritic spines and their role in the pathogenesis of neurodevelopmental and neurological disorders

Since Cajal introduced dendritic spines in the 19th century, they have attained considerable attention, especially in neuropsychiatric and neurologic disorders. Multiple roles of dendritic spine malfunction and pathology in the progression of various diseases have been reported. Thus, it is inevitable to consider these structures as new therapeutic targets for treating neuropsychiatric and neurologic disorders such as autism spectrum disorders, schizophrenia, dementia, Down syndrome, etc. Therefore, we attempted to prepare a narrative review of the literature regarding the role of dendritic spines in the pathogenesis of aforementioned diseases and to shed new light on their pathophysiology.

Initial Experience of 18 F-FET PET-MR Image Fusion for Evaluation of Recurrent Primary Brain Tumors

Background  An accurate monitoring technique is crucial in brain tumors to choose the best treatment approach after surgery and/or chemoradiation. Radiological assessment of brain tumors is widely based on the magnetic resonance imaging (MRI) modality in this regard; however, MRI criteria are unable to precisely differentiate tumoral tissue from treatment-related changes. This study was conducted to evaluate whether fused MRI and O-(2- 18 F-fluoroethyl)-L-tyrosine ( 18 F-FET) positron emission tomography (PET) can improve the diagnostic accuracy of the practitioners to discriminate treatment-related changes from true recurrence of brain tumor. Methods  We retrospectively analyzed 18 F-FET PET/computed tomography (CT) of 11 patients with histopathologically proven brain tumors that were suspicious for recurrence changes after 3 to 4 months of surgery. All the patients underwent MRI and 18 F-FET PET/CT. As a third assessment, fused 18 F-FET PET/MRI was also acquired. Finally, the diagnostic accuracy of the applied modalities was compared. Results  Eleven patients aged 27 to 73 years with a mean age of 47 ± 13 years were enrolled. According to the results, 9/11 cases (82%) showed positive MRI and 6 cases (55%) showed positive PET/CT and PET/MRI. Tumoral recurrence was observed in six patients (55%) in the follow-up period. Based on the follow-up results, accuracy, sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were 64, 85, 25, 67, and 50%, respectively, for MRI alone and 91, 85, 100, 100, and 80%, respectively, for both PET/CT and PET/MRI. Conclusion  This study found that 18 F-FET PET-MR image fusion in the management of brain tumors might improve recurrence detection; however, further well-designed studies are needed to verify these preliminary data.

The neural effects of oxytocin administration in autism spectrum disorders studied by fMRI: A systematic review

PURPOSE

Oxytocin (OXT) is a hypothalamic neuropeptide that is released from the posterior pituitary gland and at specific targets in the central nervous system (CNS). The prosocial effects of OXT acting in the CNS present it as a potential therapeutic agent for the treatment of aspects of autism spectrum disorder (ASD). In this article, we systematically review the functional MRI (fMRI) literature that reports task-state and resting-state fMRI (rsfMRI) studies of the neural effects of single or multiple dose intranasal OXT (IN-OXT) administration in individuals with ASD.

METHOD

We searched four databases for relevant documents (PubMed, Web of Science, Scopus, and Google Scholar) using the keywords "autism spectrum disorder", "Asperger Syndrome", "oxytocin", and "fMRI". Moreover, we made a manual search to assess the quality of our automatic search. The search was confined to English language articles published in the interval February 2013 until March 2021.

RESULTS

The search yielded 12 fMRI studies with OXT intervention, including 288 individuals with ASD (age 8-55 years) enrolled in randomized, double-blind, placebo-controlled, parallel designs, within-subject-crossover experimental OXT trials. Studies reporting activation task and rsfMRI were summarized with region of interest (ROI) or whole-brain voxel wise analysis. The systematic review of the 12 studies supported the proposition that IN-OXT administration alters brain activation in individuals with ASD. The effects of IN-OXT interacted with the type of the task and the overall results did not indicate restoration of normal brain activation in ASD signature regions albeit the lack of statistical evidence.

CONCLUSION

A large body of evidence consistently indicates that OXT alters activation to fMRI in brain networks of individuals with ASD, but with uncertain implications for alleviation of their social deficits.

The role of multimodal MRI in mild cognitive impairment and Alzheimer's disease

BACKGROUND AND PURPOSE

Mild cognitive impairment (MCI) is a prodromal stage of Alzheimer's disease (AD), where neurodegeneration is not as considerable, thereby potentially increasing the effect of treatments. Therefore, highly sensitive and specific classification of subjects with MCI is necessary, where various MRI modalities have displayed promise.

METHODS

Structural, diffusion, and resting-state (RS) functional MRI analyses were performed on the AD (n = 26), MCI (n = 5), and healthy control (HC) (n = 14) group. Structural analysis was performed via voxel-based morphometry (VBM) and volumetric subcortical segmentation analysis. Fractional anisotropy and mean diffusivity were estimated during the diffusion analysis. RS analysis investigated seed-based functional connectivity. Classification via support vector machine was performed to evaluate which MRI modality most accurately differentiated the groups. Multiple linear regression was conducted to evaluate the MRI modalities correlation with clinical assessment scores.

RESULTS

Classification of MCI and HC displayed highest accuracy based on diffusion MRI, which besides demonstrated high correlation with clinical scores. Classification was equally accurate in AD, when using VBM or diffusion tensor imaging measures. Yet, more variance was explained by VBM measures in the clinical assessment scores of the AD group.

CONCLUSIONS

This study highlights the potential of diffusion MRI in differentiating MCI from HC and AD. However, the results need to be interpreted with caution as sample size and artifacts in the MRI data probably influenced the results.

On the learning of addictive behavior: Sensation-seeking propensity predicts dopamine turnover in dorsal striatum

We asked if sensation-seeking is linked to premorbid personality characteristics in patients with addictive disorders, or the characteristics follow the sensation-seeking activity. We interpreted the former as a state associated with normal rates of dopamine synthesis, and the latter as a trait of individuals with abnormally high rates of synthesis. We previously determined dopaminergic receptor density in striatum, and we now tested the hypothesis that an elevated dopaminergic condition with increased extracellular dopamine and receptor density follows increased dopamine synthesis capacity in highly sensation-seeking individuals, as measured by positron emission tomography of 18 men with tracer fluorodopa (FDOPA). We detected a site in left caudate nucleus where the volume of distribution of FDOPA-derived metabolites correlated negatively with FDOPA metabolite turnover, consistent with decreased metabolite breakdown in highly sensation-seeking subjects. High rates of sensation-seeking attenuated the dopamine turnover in association with a low rate of dopamine recycling, low dopamine oxidation, and elevated extracellular dopamine and receptors in caudate nucleus. In contrast, low rates of sensation-seeking were associated with rapid dopamine recycling, rapid dopamine oxidation, low extracellular dopamine, and low receptor density. We conclude that the modulation of dopaminergic neurotransmission associated with sensation-seeking is a state of sensation-seeking, rather than a trait of personality following abnormal regulation of dopaminergic neurotransmission.

Hippocampal neurodegeneration and rhythms mirror each other during acute spinal cord injury in male rats

Spinal Cord Injury (SCI), triggers neurodegenerative changes in the spinal cord, and simultaneously alters oscillatory manifestations of motor cortex. However, these disturbances may not be limited to motor areas and other parts such as hippocampus, which is vital in the neurogenesis and cognitive function, may be affected in the neurogenic and oscillatory manners. Addressing this remarkable complication of SCI, we evaluated the hippocampal neurogenesis and rhythms through acute phase of SCI. In the present study, we used 40 male rats (Sham.W1 = 10, SCI.W1 = 10, Sham.W2 = 10, SCI.W2 = 10), and findings revealed that contusive SCI declines hippocampal rhythms (Delta, Theta, Beta, Gamma) power and max-frequency. Also, there was a significant decrease in the DCX + and BrdU + cells of the dentate gyrus; correlated significantly with rhythms power decline. Considering the TUNEL assay analysis, there were significantly greater apoptotic cells, in the CA1, CA3, and DG regions of injured animals. Furthermore, according to the western blotting analysis, the expression of receptors (NMDA, GABAA, Muscarinic1), which are essential in the neurogenesis and generation of rhythms significantly attenuated following SCI. Our study demonstrated that acute SCI, alters the power and max-frequency of hippocampal rhythms parallel with changes in the hippocampal neurogenesis, apoptosis, and receptors expression.

Dual-phase 68Ga-PSMA-11 PET/CT may increase the rate of detected lesions in prostate cancer patients

BACKGROUND

This study was conducted to compare the early static (3-6 min post-injection (p.i.)) and standard whole body (1 h, p.i.) 68Ga-PSMA-11 PET/CT imaging for detection of lesions in prostate cancer (PC) patients.

MATERIALS AND METHODS

In this study, PC patients suspected of recurrence underwent 68Ga-PSMA-11 PET/CT. Early static images were acquired from the pelvis and the lower abdomen 3-5 minutes after radiotracer injection and, a routine whole body scan was performed from the skull to the mid-thigh 1 h after injection. Quantitative analysis (SUVmax) was evaluated in suspicious lesions.

RESULTS

Of 19 evaluated PC patients with a median age of 72 ± 1.66 years (range: 55-85 years) and prostate-specific antigen (PSA) of 1.72 ± 6.11 ng/ml (range: 0.1-100 ng/ml) (median ± SE), 16 showed positive in the whole body PET/CT. All of the patients with positive whole body scans due to pelvic involvement had positive early scan results. Totally, 22 lesions were detected in both early and delay scans in the pelvic which 16 were related to prostate involvement, 4 were related to lymph node involvement, and 2 were related to bone involvement. Moreover, in addition to the mentioned 22 lesions, early PET imaging successfully detected local recurrence in a patient who was negative on WB PET/ CT; this lesion was masked in the delay scan due to bladder activity. The median SUVmax values of the early and delay scans were 3.69 ± 1.07 (median ± SE) (range: 1.2-14.5) and 5.85 ± 1.69 (range: 3.1-23.4), respectively. (p = 0.005).

CONCLUSION

Early static 68Ga-PSMA-11 PET/CT imaging might discriminate metastases from urinary bladder activity. Therefore, early static imaging in combination with whole body 60-min p.i. imaging can improve the detection of local involvement pelvic disease.

Avicenna (980-1037 CE) and his Early Description and Classification of Dementia

According to the World Health Organization (WHO), dementia is a disorder that occurs as result of a neurodegenerative process in brain, and usually is chronic or progressive by nature. Most descriptions of senile dementia date back to Alois Alzheimer. In 1906, Alzheimer described the first patient, Auguste Deter, who suffered from the disorder that later became known as Alzheimer's disease. Although, the history of the disease before 1906 is quite rich, little has been said about the contributions of ancient and medieval physicians to the understanding of dementia. Over the centuries, the concept of senile dementia changed from an inevitable mental decline with aging, to different sets of clinical features with narrow limits of diagnosis of a disease in its own right. Documentation of the historical origins of prevention, diagnosis, and therapies of dementia would make an important contribution to a more complete understanding of this pathological degeneration of dementia. The present review focuses on the contributions of Avicenna (AD 980-1037) to the development of diagnosis and the discovery of etiology of different forms of dementia, with the goal of revealing the extent to which dementia was understood in the golden age of Islam in Persia.

Comparison of cognitive flexibility, appropriate risk-taking and reaction time in individuals with and without adult ADHD

Attention Deficit Hyperactivity Disorder (ADHD) is a developmental and psychiatric disorder that affects different aspects of an individual life, such as cognitive functions. ADHD comprise a complex symptomatology such as cognitive flexibility and inappropriate risk-taking. We aimed to compare cognitive flexibility and appropriate risk-taking of adults with and without ADHD. For this purpose, the Conners' Adult ADHD Rating Scale (CAARS) was used to screen 580 students of Tehran University in Iran. Forty participants who scored highest in CAARS were invited to have a clinical interview with a trained psychiatrist. The diagnosis was made based on the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), using the Wender Utah Rating Scale (WURS). Finally, thirty individuals were diagnosed with ADHD. Meanwhile, the 30 students with the lowest scores on the CAARS and General Health Questionnaire (GHQ) were included as the control group. The two groups then were compared using the Cognitive Flexibility Inventory (CFI) and the Iowa Gambling Task (IGT). The results of the one-way ANOVA indicated that scores of case group in the components of cognitive flexibility were significantly lower in the patients compared to the control group. Also, the ADHD group had lower scores concerning appropriate risk-taking and had a shorter reaction time. Findings of the current study might help to open further avenues in the rehabilitation of cognitive flexibility and controlling reward-seeking and risk-seeking impulses.

Cerebrolysin attenuates ethanol-induced spatial memory impairments through inhibition of hippocampal oxidative stress and apoptotic cell death in rats

The present study investigates the potential neuroprotective effect of cerebrolysin (CBL), a combination of neurotrophic factors, on the cognitive and biochemical alterations induced by chronic ethanol administration in rats. The animals were divided into five groups as follows: control; ethanol (4 g/kg, for 30 days) plus normal saline (Ethanol + NS); ethanol plus CBL 1 mL/kg (Ethanol + CBL 1), ethanol plus CBL 2.5 mL/kg (Ethanol + CBL 2.5); and ethanol plus CBL 5 mL/kg (Ethanol + CBL 5). The Morris water maze (MWM) test was performed to assess cognitive impairment. The status of the lipid peroxidation marker MDA, antioxidant capacity, as well as alterations of the apoptotic factors such as Bcl-2, BAX, and cleaved caspase-9 and -3, were evaluated in the hippocampus. The results showed that CBL treatment not only normalized the increased MDA levels in the alcoholic rats and enhanced antioxidant defense, but also reduced the Bax/Bcl-2 ratio and cleaved caspase-9 and -3 in the hippocampus. These results were parallel with improvement in spatial memory performance in the MWM test. The findings of the present study provide evidence for the promising therapeutic effect of CBL in chronic ethanol consumption through counteracting oxidative stress and apoptosis markers.

Maternal SSRI exposure increases the risk of autistic offspring: A meta-analysis and systematic review

BACKGROUND

Selective serotonin reuptake inhibitors (SSRIs) are the most common antidepressants used to preclude maternal pregnancy depression. There is a growing body of literature assessing the association of prenatal exposure to SSRIs with autism spectrum disorder (ASD). The present systematic review and meta-analysis reviewed the medical literature and pooled the results of the association of prenatal exposure to SSRIs with ASD.

METHODS

Published investigations in English by June 2016 with keywords of selective serotonin reuptake inhibitors, SSRI, autism spectrum disorder, ASD, pregnancy, childhood, children, neurodevelopment were identified using databases PubMed and PMC, MEDLINE, EMBASE, SCOPUS, and Google Scholar. Cochran's Q statistic-value (Q), degree of freedom (df), and I² indices (variation in odds ratio [OR] attributable to heterogeneity) were calculated to analyze the risk of heterogeneity of the within- and between-study variability. Pooled odds ratio (OR) and 95% confidence interval (CI) were reported by a Mantel-Haenszel test.

RESULTS

There was a non-significant heterogeneity for the included studies ([Q=3.61, df=6, P=0.730], I²=0%). The pooled results showed a significant association between prenatal SSRI exposure and ASD (OR=1.82, 95% CI=1.59-2.10, Z=8.49, P=0.00).

CONCLUSION

The evidence from the present study suggests that prenatal exposure to SSRIs is associated with a higher risk of ASD.

MtDNA T4216C variation in multiple sclerosis: a systematic review and meta-analysis

MtDNA T4216C variation has frequently been investigated in Multiple Sclerosis (MS) patients; nonetheless, controversy has existed about the evidence of association of this variation with susceptibility to MS. The present systematic review and meta-analysis converge the results of the preceding publications, pertaining to association of mtDNA T4216C variation with susceptibility to MS, into a common conclusion. A computerized literature search in English was carried out to retrieve relevant publications from which required data were extracted. Using a fixed effect model, pooled odds ratio (OR), 95 % confidence interval (95 % CI), and P value were calculated for association of mtDNA T4216C variation with susceptibility to MS. The pooled results showed that there was a significant association between mtDNA T4216C variation and MS (OR = 1.38, 95 % CI = 1.13-1.67, P = 0.001). The present systematic review and meta-analysis suggest that mtDNA T4216C variation is a contributory factor in susceptibility to MS.

Regional cerebral blood flow responses to hyperventilation during sevoflurane anaesthesia studied with PET

BACKGROUND

Arterial carbon dioxide tension (PaCO(2)) is an important factor controlling cerebral blood flow (CBF) in neurosurgical patients. It is still unclear whether the hypocapnia-induced decrease in CBF is a general effect on the brain or rather linked to specific brain regions. We evaluated the effects of hyperventilation on regional cerebral blood flow (rCBF) in healthy volunteers during sevoflurane anaesthesia measured with positron emission tomography (PET).

METHODS

Eight human volunteers were anaesthetized with sevoflurane 1 MAC, while exposed to hyperventilation. During 1 MAC sevoflurane at normocapnia and 1 MAC sevoflurane at hypocapnia, one H(2)(15)O scan was performed. Statistical parametric maps and conventional regions of interest analysis were used for estimating rCBF differences.

RESULTS

Cardiovascular parameters were maintained constant over time. During hyperventilation, the mean PaCO(2) was decreased from 5.5 + or - 0.7 to 3.8 + or - 0.9 kPa. Total CBF decreased during the hypocapnic state by 44%. PET revealed wide variations in CBF between regions. The greatest values of vascular responses during hypocapnia were observed in the thalamus, medial occipitotemporal gyrus, cerebellum, precuneus, putamen and insula regions. The lowest values were observed in the superior parietal lobe, middle and inferior frontal gyrus, middle and inferior temporal gyrus and precentral gyrus. No increases in rCBF were observed.

CONCLUSIONS

This study reports highly localized and specific changes in rCBF during hyperventilation in sevoflurane anaesthesia, with the most pronounced decreases in the sub cortical grey matter. Such regional heterogeneity of the cerebral vascular response should be considered in the assessment of cerebral perfusion reserve during hypocapnia.

Low cerebral oxygen consumption and blood flow in patients with cirrhosis and an acute episode of hepatic encephalopathy

BACKGROUND & AIMS

It is unclear whether patients with hepatic encephalopathy (HE) have disturbed brain oxygen metabolism and blood flow.

METHODS

We measured cerebral oxygen metabolism rate (CMRO(2)) by using (15)O-oxygen positron emission tomography (PET); and cerebral blood flow (CBF) by using (15)O-water PET in 6 patients with liver cirrhosis and an acute episode of overt HE, 6 cirrhotic patients without HE, and 7 healthy subjects.

RESULTS

Neither whole-brain CMRO(2) nor CBF differed significantly between cirrhotic patients without HE and healthy subjects, but were both significantly reduced in cirrhotic patients with HE (P < .01). CMRO(2) was 0.96 +/- 0.07 mumol oxygen/mL brain tissue/min (mean +/- SEM) in cirrhotic patients with HE, 1.34 +/- 0.08 in cirrhotic patients without HE, and 1.35 +/- 0.05 in healthy subjects; and CBF was 0.29 +/- 0.01 mL blood/mL brain tissue/min in patients with HE, 0.47 +/- 0.02 in patients without HE, and 0.49 +/- 0.03 in healthy subjects. CMRO(2) and CBF were correlated, and both variables correlated negatively with arterial ammonia concentration. Analysis of regional values, using individual magnetic resonance co-registrations, showed that the reductions in CMRO(2) and CBF in patients with HE were essentially generalized throughout the brain.

CONCLUSIONS

The observations imply that reduced cerebral oxygen consumption and blood flow in cirrhotic patients with an acute episode of overt HE are associated with HE and not cirrhosis as such, and that the primary event in the pathogenesis of HE could be inhibition of cerebral energy metabolism by increased blood ammonia.

Effects of dose-dependent levels of isoflurane on cerebral blood flow in healthy subjects studied using positron emission tomography

BACKGROUND

In this study, we tested the hypothesis that escalating drug concentrations of isoflurane are associated with a significant decline in cerebral blood flow (CBF) in regions sub-serving conscious brain activity, including specifically the thalamus.

METHODS

Nine human volunteers received three escalating drug concentrations: 0.2, 0.4 and 1.0 MAC end-tidal inhalation. During waking, baseline and the three levels of sedation, aO PET scan was performed.

RESULTS

Isoflurane decreased the bispectral index (BIS) values dose-dependently. Cardiovascular and respiratory parameters were maintained constant over time. No significant change in global CBF was observed. Throughout all three MAC levels of sedation, isoflurane caused an increased regional cerebral blood flow (rCBF) in the anterior cingulate and decreased rCBF in the cerebellum. Initially, isoflurane (0 vs. 0.2 MAC) significantly increased relative rCBF in the medial frontal gyrus and in the nucleus accumbens. At the next level (0.2 vs. 0.4 MAC), relative rCBF was significantly increased in the caudate nucleus and decreased in the lingual gyrus and cuneus. At the last level (0.4 vs. 1 MAC), relative rCBF was significantly increased in the insula and decreased in the thalamus, the cuneus and lingual gyrus. Compared with flow distribution in awake volunteers, 1 MAC of isoflurane significantly raised relative activity in the anterior cingulate and insula regions. In contrast, a significant relative flow reduction was identified in the thalamus, the cerebellum and lingual gyrus.

CONCLUSIONS

Isoflurane, like sevoflurane, induced characteristic flow redistribution at doses of 0.2-1.0 MAC. At 1 MAC of isoflurane, rCBF decreased in the thalamus. Specific areas affected by both isoflurane and sevoflurane included the anterior cingulate, insula regions, cerebellum, lingual gyrus and thalamus.

Effects of subanaesthetic and anaesthetic doses of sevoflurane on regional cerebral blood flow in healthy volunteers. A positron emission tomographic study

BACKGROUND

We tested the hypothesis that escalating drug concentrations of sevoflurane are associated with a significant decline of cerebral blood flow in regions subserving conscious brain activity, including specifically the thalamus.

METHODS

Nine healthy human volunteers received three escalating doses using 0.4%, 0.7% and 2.0% end-tidal sevoflurane inhalation. During baseline and each of the three levels of anaesthesia one PET scan was performed after injection of . Cardiovascular and respiratory parameters were monitored and electroencephalography and bispectral index (BIS) were registered.

RESULTS

Sevoflurane decreased the BIS values dose-dependently. No significant change in global cerebral blood flow (CBF) was observed. Increased regional CBF (rCBF) in the anterior cingulate (17-21%) and decreased rCBF in the cerebellum (18-35%) were identified at all three levels of sedation compared to baseline. Comparison between adjacent levels sevoflurane initially (0 vs. 0.2 MAC) decreased rCBF significantly in the inferior temporal cortex and the lingual gyrus. At the next level (0.2 MAC vs. 0.4 MAC) rCBF was increased in the middle temporal cortex and in the lingual gyrus, and decreased in the thalamus. At the last level (0.4 MAC vs. 1 MAC) the rCBF was increased in the insula and decreased in the posterior cingulate, the lingual gyrus, precuneus and in the frontal cortex.

CONCLUSION

At sevoflurane concentrations at 0.7% and 2.0% a significant decrease in relative rCBF was detected in the thalamus. Interestingly, some of the most profound changes in rCBF were observed in structures related to pain processing (anterior cingulate and insula).

Focal changes of oxygen consumption in cerebral cortex of patients with Parkinson's disease during subthalamic stimulation

Motor symptoms of Parkinson's disease (PD) are substantially improved by bilateral high-frequency electrical stimulation of the subthalamic nucleus (STN). Altered cerebral blood flow (CBF) in a network of frontal cortical and subcortical structures has been reported in numerous studies of patients undergoing subthalamic stimulation. However, CBF is a controversial indicator of brain activation because measures of blood flow bear a variable relation to measures of brain work and energy metabolism. We hypothesized that STN stimulation would alter the rate of oxygen consumption (CMRO(2)) in cerebral cortical areas in proportion to previously reported changes in CBF in patients undergoing stimulation at rest. We used quantitative PET to map CMRO(2) in brain of seven patients with Parkinson's disease, first in a baseline condition with pause of stimulation and medication for a period of 12 h, and again after 4 h of stimulation. Comparison of these two conditions revealed activation of CMRO(2) in the cerebellum, and in specific posterior neocortical regions, most notably in the left lingual gyrus and in the right lateral occipitotemporal gyrus, both of which latter regions are linked to higher-order visual processing. CMRO(2) was unaffected in the frontal cortex. Thus, the present findings do not support the original hypothesis, but suggest that STN stimulation increases energy metabolism in the posterior cerebral cortex, especially in regions involved in perception of movement and the direction of movement to visual cues.

Impaired activation of oxygen consumption and blood flow in visual cortex of patients with mitochondrial encephalomyopathy

A current hypothesis claims that an increase of blood flow is required for oxygen consumption to rise during neuronal excitation (activation). Chronic progressive external ophthalmoplegia is a mitochondrial disease associated with deletions of mtDNA or by point mutation of tRNA genes. We tested the hypothesis that the cerebral metabolic rate of oxygen (CMRO2) may not rise in this disorder if the accompanying cerebral blood flow increase is insufficient. Two patients with progressive external ophthalmoplegia were visually stimulated with a colored checkerboard pattern reversing as different frequencies. When stimulated, Patient 1 had a small increase of cerebral blood flow, while Patient 2 had no cerebral blood flow increase. In the visually active state, the patients had no significant change of CMRO2, while healthy subjects had a pronounced increase of CMRO2 in the pericalcarine visual cortex at 4 Hz and a further slight increase at 8 Hz during activation.

Model of blood-brain transfer of oxygen explains nonlinear flow-metabolism coupling during stimulation of visual cortex

The coupling between cerebral metabolic rate of oxygen (CMRO2) and blood flow (CBF) in response to visual stimulation was evaluated by means of a model of oxygen delivery. The model predicted a nonlinear relationship between stimulus-evoked changes of oxygen consumption and blood flow. The magnitude of the CMRO2/CBF ratio index (IO2) was used to indicate the degree of flow-metabolism coupling prevailing in specific areas of the brain during physiological stimulation. Therefore, the index provided a measure of the blood oxygenation level dependent (BOLD) magnetic resonance contrast. To evaluate the changes of IO2 in response to visual stimulation, the model was applied to the effect of a changing flicker rate of a visual stimulus on the magnitudes of CBF, CMRO2, and oxygen diffusion capacity, in the human brain. Positron emission tomography (PET) was used to measure the CBF and the CMRO2 in 12 healthy volunteers who viewed a cross-hair (baseline) or a yellow-blue annular checkerboard reversing at frequencies of 1, 4, or 8 Hz. The magnitude of CBF in the primary visual cortex increased as a function of the checkerboard reversal rate and reached a maximum at the frequency of 8 Hz (z=16.0), while the magnitude of CMRO2 reached a maximum at 4 Hz (z=4.0). Therefore, the calculated IO2 was lower at 8 Hz than at 1 and 4 Hz, in contrast to the oxidative metabolic rate that reached its maximum at 4 Hz. The model explained the increase of oxygen consumption as the combined effect of increased blood flow and increased oxygen diffusion capacity in the region of visual activation.

Frequency-dependent changes in cerebral metabolic rate of oxygen during activation of human visual cortex

To test the hypothesis that brain oxidative metabolism is significantly increased upon adequate stimulation, we varied the presentation of a visual stimulus to determine the frequency at which the metabolic response would be at maximum. The authors measured regional CMR(O2) in 12 healthy normal volunteers with the ECAT EXACT HR+ (CTI/Siemens, Knoxville, TN, U.S.A.) three-dimensional whole-body positron emission tomograph (PET). In seven successive activating conditions, subjects viewed a yellow-blue annular checkerboard reversing its contrast at frequencies of 0, 1, 4, 8, 16, 32, and 50 Hz. Stimulation began 4 minutes before and continued throughout the 3-minute dynamic scan. In the baseline condition, the subjects began fixating a cross hair 30 seconds before the scan and continued to do so for the duration of the 3-minute scan. At the start of each scan, the subjects inhaled 20 mCi of (15)O-O2 in a single breath. The CMR(O2) value was calculated using a two-compartment, weighted integration method. Normalized PET images were averaged across subjects and coregistered with the subjects' magnetic resonance imaging in stereotaxic space. Mean subtracted image volumes (activation minus baseline) of CMR(O2) then were obtained and converted to z statistic volumes. The authors found a statistically significant focal change of CMR(O2) in the striate cortex (x = 9; y = -89; z = -1) that reached a maximum at 4 Hz and dropped off sharply at higher stimulus frequencies.

Increased oxygen consumption in human visual cortex: response to visual stimulation

To test whether a sufficiently complex visual stimulus causes the consumption of oxygen to rise in the human visual cortex, we used positron emission tomography (PET) to measure the cerebral metabolic rate of oxygen (CMRO2) during visual stimulation in 6 healthy normal volunteers. A yellow-blue checkerboard, reversing its contrast at a frequency of 8 Hz, was presented for a period of 7 min, beginning 4 min before the onset of a 3-min scan. In the baseline condition, subjects fixated a cross-hair from 30 s before until the end of the 3-min scan. The CMRO2 was calculated with the two-compartment weighted integration method (1). The checkerboard minus baseline subtraction yielded statistically significant increases in CMRO2 in the primary (V1) and higher order visual cortices (V4 and V5). The significant CMRO2 increases were detected in these regions in both the group average and in each individual subject.