Coupling between Pyroelectricity and Built-In Electric Field Enabled Highly Sensitive Infrared Phototransistor Based on InSe/WSe2/P(VDF-TrFE) Heterostructure

The assorted utilization of infrared detectors induces the demand for more comprehensive and high-performance electronic devices that work at room temperature. The intricacy of the fabrication process with bulk material limits the exploration in this field. However, two-dimensional (2D) materials with a narrow band gap opening aid in infrared (IR) detection relatively, but the photodetection range is narrowed due to the inherent band gap. In this study, we report an unprecedented attempt at the coordinated use of both 2D heterostructure (InSe/WSe₂) and the dielectric polymer (poly(vinylidene fluoride-trifluoroethylene), P(VDF-TrFE)) for both visible and IR photodetection in a single device. The remnant polarization due to the ferroelectric effect of the polymer dielectric enhances the photocarrier separation in the visible range, resulting in high photoresponsivity. On the other hand, the pyroelectric effect of the polymer dielectric causes a change in the device current due to the increased temperature induced by the localized heating effect of the IR irradiation, which results in the change of ferroelectric polarization and induces the redistribution of charge carriers. In turn, it changes the built-in electric field, the depletion width, and the band alignment across the p-n heterojunction interface. Consequently, the charge carrier separation and the photosensitivity are therefore enhanced. Through the coupling between pyroelectricity and built-in electric field across the heterojunction, the specific detectivity for the photon energy below the band gap of the constituent 2D materials can reach up to 10¹¹ Jones, which is better than all reported pyroelectric IR detectors. The proposed approach combining the ferroelectric and pyroelectric effects of the dielectric as well as exceptional properties of the 2D heterostructures can spark the design of advanced and not-yet realized optoelectronic devices.

A Bi-Anti-Ambipolar Field Effect Transistor

Multistate logic is recognized as a promising approach to increase the device density of microelectronics, but current approaches are offset by limited performance and large circuit complexity. We here demonstrate a route toward increased integration density that is enabled by a mechanically tunable device concept. Bi-anti-ambipolar transistors (bi-AATs) exhibit two distinct peaks in their transconductance and can be realized by a single 2D-material heterojunction-based solid-state device. Dynamic deformation of the device reveals the co-occurrence of two conduction pathways to be the origin of this previously unobserved behavior. Initially, carrier conduction proceeds through the junction edge, but illumination and application of strain can increase the recombination rate in the junction sufficiently to support an alternative carrier conduction path through the junction area. Optical characterization reveals a tunable emission pattern and increased optoelectronic responsivity that corroborates our model. Strain control permits the optimization of the conduction efficiency through both pathways and can be employed in quaternary inverters for future multilogic applications.

Stoichiometry-Controlled MoxW1-xTe2 Nanowhiskers: A Novel Electrocatalyst for Pt-Free Dye-Sensitized Solar Cells

Novel polymorphic Mo_xW_1-xTe₂-based counter electrodes possess high carrier mobility, phase-dependent lattice distortion, and surface charge density wave to boost the charge-transfer kinetics and electrocatalytic activity in dye-sensitized solar cells (DSSCs). Here, we report the syntheses of stoichiometry-controlled binary and ternary Mo_xW_1-xTe₂ nanowhiskers directly on carbon cloth (CC), denoted by Mo_xW_1-xTe₂/CC, with an atmospheric chemical vapor deposition technique. The synthesized Mo_xW_1-xTe₂/CC samples, including 1T'-MoTe₂/CC, T_d-WTe₂/CC, T_d-Mo_0.26W_0.73Te_2.01/CC, and 1T'- & T_d-Mo_0.66W_0.32Te_2.02/CC, were then employed as different counter electrodes to study their electrochemical activities and efficiencies in DSSCs. The photovoltaic parameter analysis manifests that Mo_xW_1-xTe₂/CCs are more stable than a standard Pt/CC in the I^-/I₃^- electrolyte examined by cyclic voltammetry over 100 cycles. A 1T'- & T_d-Mo_0.66W_0.32Te_2.02/CC-based DSSC can achieve a photocurrent density of 16.29 mA cm^-2, a maximum incident photon-to-electron conversion efficiency of 90% at 550 nm excitation, and an efficiency of 9.40%, as compared with 8.93% of the Pt/CC counterpart. Moreover, the 1T'- & T_d-Mo_0.66W_0.32Te_2.02/CC shows lower charge-transfer resistance (0.62 Ω cm²) than a standard Pt/CC (1.19 Ω cm²) in electrocatalytic reactions. Notably, Mo_xW_1-xTe₂ nanowhiskers act as an electron expressway by shortening the path of carrier transportation in the axial direction from a counter electrode to electrolytic ions to enhance the reaction kinetics in DSSCs. This work demonstrates that the nanowhisker-structured 1T'- & T_d-Mo_0.66W_0.32Te_2.02/CC with high carrier mobility and robust surface states can serve as a highly efficient counter electrode in DSSCs to replace the conventional Pt counter electrode for electrocatalytic applications.

Modulating Charge Separation with Hexagonal Boron Nitride Mediation in Vertical Van der Waals Heterostructures

Tuning the optical and electrical properties by stacking different layers of two-dimensional (2D) materials enables us to create unusual physical phenomena. Here, we demonstrate an alternative approach to enhance charge separation and alter physical properties in van der Waals heterojunctions with type-II band alignment by using thin dielectric spacers. To illustrate our working principle, we implement a hexagonal boron nitride (h-BN) sieve layer in between an InSe/GeS heterojunction. The optical transitions at the junctions studied by photoluminescence and the ultrafast pump-probe technique show quenching of emission without h-BN layers exhibiting an indirect recombination process. This quenching effect due to strong interlayer coupling was confirmed with Raman spectroscopic studies. In contrast, h-BN layers in between InSe and GeS show strong enhancement in emission, giving another degree of freedom to tune the heterojunction property. The two-terminal photoresponse study supports the argument by showing a large photocurrent density for an InSe/h-BN/GeS device by avoiding interlayer charge recombination. The enhanced charge separation with h-BN mediation manifests a photoresponsivity and detectivity of 9 × 10² A W^-1 and 3.4 × 10¹⁴ Jones, respectively. Moreover, a photogain of 1.7 × 10³ shows a high detection of electrons for the incident photons. Interestingly, the photovoltaic short-circuit current is switched from positive to negative, whereas the open-circuit voltage changes from negative to positive. Our proposed enhancement of charge separation with 2D-insulator mediation, therefore, provides a useful route to manipulate the physical properties of heterostructures and for the future development of high-performance optoelectronic devices.

Sn-Doping Enhanced Ultrahigh Mobility In1-xSnxSe Phototransistor

Two-dimensional ternary materials are attracting widespread interest because of the additional degree of freedom available to tailor the material property for a specific application. An In_1-xSn_xSe phototransistor possessing tunable ultrahigh mobility by Sn-doping engineering is demonstrated in this study. A striking feature of In_1-xSn_xSe flakes is the reduction in the oxide phase compared to undoped InSe, which is validated by spectroscopic analyses. Moreover, first-principles density functional calculations performed for the In_1-xSn_xSe crystal system reveal the same effective mass when doped with Sn atoms. Hence, because of an increased lifetime owing to the enhanced crystal quality, the carriers in In_1-xSn_xSe have higher mobility than in InSe. The internally boosted electrical properties of In_1-xSn_xSe exhibit ultrahigh mobility of 2560 ± 240 cm² V^-1 s^-1 by suppressing the interfacial traps with substrate modification and channel encapsulation. As a phototransistor, the ultrathin In_1-xSn_xSe flakes are highly sensitive with a detectivity of 10¹⁴ Jones. It possesses a large photoresponsivity and photogain (V_g = 40 V) as high as 3 × 10⁵ A W^-1 and 0.5 × 10⁶, respectively. The obtained results outperform all previously reported performances of InSe-based devices. Thus, the doping-engineered In_1-xSn_xSe-layered semiconductor finds a potential application in optoelectronics and meets the demand for faster electronic technology.

Ultra-high performance flexible piezopotential gated In1-xSnxSe phototransistor

Flexible optoelectronic devices facilitated by the piezotronic effect have important applications in the near future in many different fields ranging from solid-state lighting to biomedicine. Two-dimensional materials possessing extraordinary mechanical strength and semiconducting properties are essential for realizing nanopiezotronics and piezo-phototronics. Here, we report the first demonstration of piezo-phototronic properties in In_1-xSn_xSe flexible devices by applying systematic mechanical strain under photoexcitation. Interestingly, we discover that the dark current and photocurrent are increased by five times under a bending strain of 2.7% with a maximum photoresponsivity of 1037 AW^-1. In addition, the device can act as a strain sensor with a strain sensitivity up to 206. Based on these values, the device outperforms the same class of devices in two-dimensional materials. The underlying mechanism responsible for the discovered behavior can be interpreted in terms of piezoelectric potential gating, allowing the device to perform like a phototransistor. The strain-induced gate voltage assists in the efficient separation of photogenerated charge carriers and enhances the mobility of In_1-xSn_xSe, resulting in good performance on a freeform surface. Thus, our multifunctional device is useful for the development of a variety of advanced applications and will help meet the demand of emerging technologies.

High photosensitivity and broad spectral response of multi-layered germanium sulfide transistors

In this paper, we report the optoelectronic properties of multi-layered GeS nanosheet (∼28 nm thick)-based field-effect transistors (called GeS-FETs). The multi-layered GeS-FETs exhibit remarkably high photoresponsivity of Rλ ∼ 206 A W(-1) under 1.5 μW cm(-2) illumination at λ = 633 nm, Vg = 0 V, and Vds = 10 V. The obtained Rλ ∼ 206 A W(-1) is excellent as compared with a GeS nanoribbon-based and the other family members of group IV-VI-based photodetectors in the layered-materials realm, such as GeSe and SnS2. The gate-dependent photoresponsivity of GeS-FETs was further measured to be able to reach Rλ ∼ 655 A W(-1) operated at Vg = -80 V. Moreover, the multi-layered GeS photodetector holds high external quantum efficiency (EQE ∼ 4.0 × 10(4)%) and specific detectivity (D* ∼ 2.35 × 10(13) Jones). The measured D* is comparable to those of the advanced commercial Si- and InGaAs-based photodiodes. The GeS photodetector also shows an excellent long-term photoswitching stability over a long period of operation (>1 h). These extraordinary properties of high photocurrent generation, broad spectral range, and long-term stability make the GeS-FET photodetector a highly qualified candidate for future optoelectronic applications.

Regional cerebral blood flow and depersonalization after tetrahydrocannabinol administration

OBJECTIVE

The aim of this study was to examine the relationship between depersonalization induced by tetrahydrocannabinol (THC), and regional brain activation.

METHOD

Cerebral blood flow (CBF) was measured by means of positron emission tomography (PET) in 59 normal right-handed volunteers before and following intravenous infusions of THC.

RESULTS

After THC, CBF showed a global increase which was more marked in the right hemisphere, frontal lobes and anterior cingulate.

CONCLUSION

Regression analyses showed positive correlations between the right frontal and anterior cingulate and depersonalization.

Cerebellar activity and disturbed time sense after THC

Because marijuana continues to be the most commonly used illicit drug, its effects on the brain function are of major interest. We utilized positron emission tomography (PET) and magnetic resonance imaging (MRI) to study the effects of delta-9-tetrahydrocannabinol (THC) infusion on brain blood flow and its behavioral correlates in 46 volunteers. Consistent with previous reports, there was a significant increase in cortical and cerebellar blood flow following THC, but not all subjects showed this effect. Those who showed a decrease in cerebellar CBF also had a significant alteration in time sense. The relationship between decreased cerebellar flow and impaired time sense is of interest because the cerebellum has been linked to an internal timing system.

Intracranial and extracranial blood flow during acute anxiety

While large numbers of studies are available on anxiety and cerebral blood flow (CBF), little is known about their relationship to extracranial (forehead) flow. The participants were 24 generalized anxiety disorder (GAD) patients and 26 normal volunteers. A randomized, between groups, repeated measures design was used to evaluate changes in cerebral blood flow. Measurements of CBF, forehead skin perfusion and ratings of anxiety and physiologic indices were made under resting conditions and during anxiety induction with epinephrine or saline infusions, given under double-blind conditions while subjects inhaled room air or 5% CO2. These subjects were divided into three groups; those with decreased anxiety, those with mild anxiety, and those with more severe anxiety increase. Subjects with severe anxiety showed least hypercarbic CBF increase (indicating cerebral vasoconstriction) and maximal increase in forehead skin perfusion. Those with minimal anxiety had most hypercarbic cerebral vasodilation and least increase in forehead skin perfusion. Forehead skin perfusion correlated positively with anxiety levels, and negatively with hypercarbic cerebral vasodilation. In animals, sympathetic activation limits hypercapnic cerebral vasodilation. Thus, the restricted hypercapnic cerebral vasodilation during severe anxiety may be mediated through cervical sympathetic fibers which innervate cerebral vessels.

Effect of nitrous oxide on cerebral blood velocity while reclining and standing

Cerebral blood velocity (CBV) (measured with transcranial Doppler, TCD) and other physiological and rating scale indices were measured before, during, and after inhaling a mixture of 40% nitrous oxide/oxygen and 40% nitrogen/oxygen, given during two separate visits in 7 normal male volunteers. During nitrous oxide/oxygen but not nitrogen/oxygen inhalation, CBV and euphoria increased significantly with minimal changes in other physiological indices except an increase in pulse rate after nitrous oxide/oxygen. In another 7 male volunteers, similar measurements were obtained while lying down and standing up during nitrous oxide/oxygen mixture and nitrogen/oxygen mixture inhalations, given during two separate visits. Nitrous oxide/oxygen inhalation produced significant CBV increase, which showed nonsignificant decrease of no clinical significance during standing up. There were no significant postural changes in blood pressure. Standing up during nitrous oxide/oxygen inhalation was associated with significant though mild dizziness.

Cerebral vasodilation and vasoconstriction associated with acute anxiety

A randomized, between-groups, repeated measures design was used to evaluate changes in cerebral blood flow (CBF), rating scales, and physiologic indices under resting conditions, during 5% CO2 inhalation in combination with epinephrine or saline infusions, in generalized anxiety disorder patients and controls. Subjects were divided into those with decreased anxiety and mild and more severe anxiety increase. The first group was found to have most pronounced CBF increase during CO2 inhalation, with the second group showing less marked increase, and the last group the least increase. In animals, sympathetic activation limits hypercapnic cerebral vasodilation. Thus, the restricted hypercapnic cerebral vasodilation during severe anxiety may be mediated through cervical sympathetic fibers, which innervate cerebral vessels.

Marijuana intoxication and brain activation in marijuana smokers

OBJECTIVE AND METHOD

The acute effects of delta9 tetrahydrocannabinol (THC) on cerebral blood flow (CBF) were studied in human subjects. Regional CBF was measured with 15O-water and Positron Emission Tomography (PET) in 32 volunteers with a history of exposure to marijuana. Scans were performed before and after intravenous (I.V.) infusion of either of two doses of THC or a placebo, given under double blind conditions.

RESULTS

THC but not placebo increased CBF especially in the frontal regions bilaterally, insula and cingulate gyrus and sub-cortical regions with somewhat greater effects in the right hemisphere. While most regions showed significant change at 60 minutes for the lower dose group, the higher dose group had significant change at 30 and 60 minutes. There was a highly significant change in the anterior/posterior ratio for the two THC groups reflecting minimal change in occipital flow but significant increases in frontal flow. Self ratings of THC intoxication showed significant effects, and regression analysis indicated it correlated most markedly with the right frontal region.

CONCLUSION

Behavioral manifestations of marijuana intoxication may be associated with increased functional activity of the brain especially the frontal cortex, insula and cingulate gyrus.

Acute changes in cranial blood flow after cocaine hydrochloride

Cerebral blood flow (CBF) was measured with the 133Xenon inhalation technique and forehead skin flow with laser Doppler, before and twice after 0.3 milligram/kilogram of cocaine hydrochloride and a placebo given intravenously to six cocaine abusers, during two visits, separated by a minimum of one week. After cocaine, subjects showed significant increases in intoxication and tension. Systolic blood pressure and pulse rate also increased significantly after the drug but not after the placebo. CBF, with and without correction for end-tidal CO2, showed increases in left and right hemisphere after cocaine. The CBF increase was maximal in frontal, central and parietal regions. CBF changes correlated only with changes in a rated level of intoxication. Forehead skin flow did not change after cocaine or placebo. In habitual cocaine abusers, 0.3 mg/kg of cocaine, given intravenously produced increased CBF and no changes in forehead skin flow.

A retrospective study of the concept of spirituality as understood by recovering individuals

In 62 individuals recovering from substance abuse, materialism and spiritualism and cognitive patterns were quantified, before (retrospectively) and after recovery with the Mathew Materialism Spiritualism Scale (MMSS) and a Cognitive Patterns Questionnaire (CPQ). MMSS was also administered once to 61 general controls. Recovering individuals showed highly significant prerecovery to postrecovery increases in spirituality on most subscales of MMSS and changes in cognitive patterns. Sixteen controls who met the criteria for alcoholism on the Michigan Alcoholism Screening Test (MAST-positive) were separated from the others. Prerecovery MMSS scores did not differentiate the recovering individuals from MAST-positive controls. However, the prerecovery MMSS scores obtained by recovering individuals were significantly lower than the scores obtained by the MAST-negative controls. On the other hand, after recovery, recovering individuals showed higher MMSS spirituality scores in comparison to MAST-positive controls. The only MMSS item that differentiated recovering individuals after recovery from MAST-negative controls was mysticism with the recovering group obtaining higher scores.

Measurement of materialism and spiritualism in substance abuse research

OBJECTIVE

A modified version of an instrument called the Mathew Materialism-Spiritualism Scale (MMSS), originally developed in India, was evaluated for possible use in substance abuse research in the U.S.

METHOD

The scale was administered to 62 individuals recovering from substance use, 20 clergy people and 61 general controls.

RESULTS

Test-retest reliability for the MMSS was verified by administering it to 18 control subjects on two separate occasions, 7 days apart. The Pearson correlation for the MMSS total scores was 0.83 (p < .0001). Internal consistency was examined with Cronbach's alpha in the entire sample of 143 subjects; the result for the total score was .93. Factor analysis showed a factor structure compatible with the subscales proposed by the developer. Women, in general, obtained higher spirituality scores. Members of the recovering group obtained significantly higher scores on "character" and "mysticism" than the general controls. When general controls were divided into MAST positive and MAST negative individuals, the MAST positive group obtained lower scores than the recovering group for "God," "mysticism" and "character." MAST negative individuals had lower scores on "mysticism" than the recovering group. Christians had higher scores on "God" and "religion" subscales than did nonChristians and agnostics.

CONCLUSIONS

The results of this study need confirmation using an improved methodology and larger sample sizes. However, they suggest that the scale may be useful for the study of spirituality in the U.S.

Cerebral blood flow and metabolism in anxiety and anxiety disorders

Anxiety disorders are some of the commonest psychiatric disorders and anxiety commonly co-exists with other psychiatric conditions. Anxiety can also be a normal emotion. Thus, study of the neurobiological effects of anxiety is of considerable significance. In the normal brain, cerebral blood flow (CBF) and metabolism (CMR) serve as indices of brain function. CBF/CMR research is expected to provide new insight into alterations in brain function in anxiety disorders and other psychiatric disorders. Possible associations between stress I anxiety I panic and cerebral ischemia I stroke give additional significance to the effects of anxiety on CBF. With the advent of non-invasive techniques, study of CBF/CMR in anxiety disorders became easier. A large numbers of research reports are available on the effects of stress, anxiety and panic on CBF/CMR in normals and anxiety disorder patients. This article reviews the available human research on this topic.

Effects of marijuana on performance of a computerized cognitive-neuromotor test battery

To evaluate the sensitivity of a computerized cognitive-neuromotor test battery in assessing the effects of marijuana (delta-9-tetrahydrocannabinol [THC]), we conducted a study of 10 healthy male volunteers who were experienced marijuana smokers. After extensive training on the performance tasks, each subject was tested on three separate days after smoking a cigarette containing either 1.75% THC, 3.55% THC, or placebo according to a randomized double-blind repeated measures design. Testing was carried out before smoking and 30, 90, and 150 minutes after smoking the cigarette. Of the five tasks employed, the digit-symbol substitution test with memory and the reaction time task were the measures most sensitive to effects of marijuana. We examined the usefulness of the coefficient of variation and effect size as indices of sensitivity to be used across different types of tasks.

Asymmetry of rCBF in schizophrenia: relationship to AP-gradient and duration of illness

This article examines patients with schizophrenia and controls to determine whether asymmetry and anteroposterior (AP) gradient of cerebral blood flow (CBF) are related to duration of illness, and whether they are themselves correlated. CBF was measured with the 133xenon inhalation technique in 108 patients and 108 age-matched and gender-matched controls while the subjects were at rest. Two sets of analyses were performed. The first analyses indicated AP-gradient to be reduced in patients, and hemispheric asymmetry scores to be different from controls only in the temporal area. The second set of analyses were based on two groups of 27 patients, selected to represent extremes on duration of illness (less than 5 and greater than 12 years) and equal numbers of age-matched and gender-matched controls. These analyses revealed patients of both short and long duration of illness to have significantly greater temporal asymmetry, whereas only long-duration patients had significant AP-gradient relative to both controls and short-duration patients. Regression analyses from each data set found AP-gradient to be related to duration of illness, whereas temporal asymmetry was not, temporal asymmetry and AP-gradient were not correlated. These results suggest AP-gradient and temporal asymmetry may reflect independent processes.

Psychiatric disorders in adult children of alcoholics: data from the Epidemiologic Catchment Area project

OBJECTIVE

The authors examined differences in the prevalence of psychiatric disorders in individuals who did or did not have alcoholic parents.

METHOD

They used data from the National Institute of Mental Health Epidemiologic Catchment Area project, specifically from the Piedmont of North Carolina. Prevalence of psychiatric disorders was estimated in 408 ECA participants who reported problem drinking in their mother, their father, or both and in 1,477 age- and sex-matched subjects who did not report having alcoholic parents.

RESULTS

The adult children of alcoholics showed significantly higher current (6-month) prevalence rates of simple phobia and agoraphobia and lifetime rates of dysthymia, generalized anxiety disorder, panic disorder, simple phobia, and agoraphobia. Adult children of alcoholics also had significantly more antisocial symptoms. Male children of alcoholics had higher rates of alcohol and drug abuse and reported more antisocial symptoms than did female children of alcoholics. Male children of alcoholics had a significantly higher rate of lifetime diagnoses of alcohol and drug abuse than men who were not children of alcoholics. More female children of alcoholics had generalized anxiety disorder than women who were not children of alcoholics. Both male and female children of alcoholics had significantly more antisocial symptoms than their matched comparison subjects. Sons of alcoholic fathers had a higher rate of substance abuse and more antisocial symptoms than did daughters of alcoholic fathers. Daughters of alcoholic fathers had a higher rate of generalized anxiety disorder.

CONCLUSIONS

These data on adult children of alcoholics in a large community sample add to a literature based mainly on descriptive material or studies of smaller samples.

Depersonalization after marijuana smoking

Depersonalization and other behavioral and physiological indices were monitored before and after the administration of high- and low-potency marijuana cigarettes and a placebo cigarette in 35 physically and mentally healthy normal volunteers. The cigarettes were administered under double-blind conditions during three visits to the laboratory separated by a minimum of 1 week. Marijuana smoking, but not placebo smoking, was associated with significant depersonalization that was maximal 30 min after smoking the high-potency cigarettes. Other behavioral changes induced by marijuana included disintegration of time sense, sensation of "high," increased state anxiety, tension, anger, and confusion. Respiration, pulse rate, and systolic blood pressure also increased after marijuana smoking. Multiple regression identified temporal disintegration as the most significant predictor of depersonalization.

Acute changes in cerebral blood flow after smoking marijuana

In experienced marijuana smokers, marijuana smoking was accompanied by a significant bilateral increase in cerebral blood flow (CBF) especially in the frontal regions and cerebral blood velocity. The post-marijuana CBF increase could not be explained on the basis on changes in general circulation or respiration. Similarly, the CBF increase was unrelated to plasma levels of tetrahydrocannabinol and extracranial circulation. Behavioral changes showed significant correlations with CBF. CBF and brain function are closely coupled and therefore it seemed highly likely that CBF changes after marijuana were closely related to its effect on mood and behavior.

Regional cerebral blood flow after marijuana smoking

Regional CBF was measured with the 133Xe inhalation technique before and thrice after smoking marijuana of two strengths and placebo in 20 physically and mentally healthy male volunteers with a previous history of exposure to marijuana. They were drug-free at the time of the study. Blood pressure, pulse rate, end-tidal carbon dioxide, end-tidal carbon monoxide, and forehead skin perfusion were quantified during the CBF measurements. Blood samples were drawn for quantification of plasma levels of delta 9-tetrahydrocannabinol (THC) before and during the 2 h after smoking marijuana or placebo. Drug-induced intoxication and changes in mood were quantified with rating scales. Marijuana smoking was associated with bilateral CBF increase, which was maximal 30 min later. Greater CBF increases were seen in the frontal region and right hemisphere. No significant CBF changes were seen after placebo. Pulse rate and respiration increased significantly after marijuana but not placebo. Both marijuana and placebo smoking were associated with increased end-tidal carbon monoxide. CBF increase in both hemispheres correlated significantly with degree of intoxication, plasma levels of THC, and pulse rate.

Middle cerebral artery velocity during upright posture after marijuana smoking

Marijuana is known to cause symptoms suggestive of orthostatic hypotension such as dizziness and fainting during upright posture. We examined changes in cerebral blood velocity (CBV) and peripheral circulation during upright posture after smoking marijuana in 10 right-handed male subjects with a previous history of exposure to marijuana. The participants were physically and mentally healthy and drug-free for a minimum of 3 months before the experiment. Middle cerebral artery CBV, blood pressure and pulse rate were recorded during reclining position and standing, before and after smoking a high-potency marijuana cigarette or a placebo cigarette administered during 2 separate visits to the laboratory. The participants were questioned about dizziness during the upright position. Six of 10 subjects reported moderate to severe dizziness during standing after marijuana but not placebo. Subjects who experienced severe dizziness during standing showed marked decreases in blood pressure and CBV. Those who reported moderate dizziness showed reduction in CBV but not blood pressure. Subjects who reported mild dizziness after marijuana and after placebo smoking showed minimal changes in blood pressure and CBV. Cerebral ischemia during upright position after marijuana smoking may be caused by hypotension and impaired cerebral autoregulation.

Changes in middle cerebral artery velocity after marijuana

Velocity of blood flow in the middle cerebral artery was measured with transcranial Doppler flowmeter before, during, and 1 hr after smoking a marijuana cigarette and a placebo cigarette during two separate visits to the laboratory. Ten healthy, right-handed male volunteers with a history of marijuana smoking took part in the study. The participants were drug-free for a minimum of 3 mo before the project. During the experiment, blood pressure, pulse rate, and end tidal levels of carbon dioxide were continually monitored. Marijuana smoking was associated with a significant increase in middle cerebral artery velocity. Although marijuana smoking was associated with increased pulse rate, the changes in blood velocity and pulse rate followed different time courses. Marijuana smoking was not associated with significant changes in blood pressure or end tidal carbon dioxide.

Changes in cerebral blood velocity after intravenous diazepam

Cerebral blood velocity (CBV) was measured with transcranial Doppler in 6 normal right-handed male volunteers before and for 50 min after an intravenous injection of 0.1 mg/kg of diazepam and normal saline during 2 separate visits to the laboratory. Blood pressure, pulse rate, end tidal levels of carbon dioxide and mood changes were quantified before and after the injections. Diazepam injection was associated with significant increases in fatigue and sleepiness. There were no significant changes in end tidal carbon dioxide, respiration, pulse rate, and blood pressure after the injection. Postdiazepam CBV was significantly lower following diazepam compared to CBV following placebo.

Evaluation of the effects of diazepam and an experimental anti-anxiety drug on regional cerebral blood flow

In the normal brain, cerebral blood flow (CBF) and function are closely coupled. Thus, changes in brain function associated with drug-induced anxiety reduction should be accompanied by parallel CBF changes. Benzodiazepines such as diazepam have been reported to reduce CBF. It is unclear, however, if this CBF decrease is specifically a function of the anti-anxiety property of the drug. To examine the relationship between drug-induced anxiety reduction and CBF changes more closely, i.v. injections of an established anxiolytic agent and an experimental anti-anxiety drug were given to patients with generalized anxiety disorder. CBF and anxiety levels were measured before and 30 min after i.v. administration of diazepam (0.12 mg/kg), ondansetron (0.24 mg/kg), and normal saline during separate visits to the laboratory. The order of drug administration was randomized, and the injections were given under double-blind conditions. Diazepam but not ondansetron or saline reduced anxiety. Global CBF reduction was seen after diazepam, but no changes were found following the other two experimental conditions. The CBF values were adjusted for test-retest changes in carbon dioxide levels. Postdiazepam decreases in CBF and anxiety levels did not correlate.

Substance abuse and cerebral blood flow

OBJECTIVE AND METHOD

This paper reviews acute and chronic effects of drugs of abuse on cerebral blood flow (CBF) and metabolism and their clinical significance. The most important source of information for the review is human research reports published in refereed journals. A few animal studies, book chapters, and abstracts that are especially relevant are also included.

RESULTS

In humans, ethanol in small doses produces cerebral vasodilation; higher doses induce cerebral vasoconstriction. Chronic alcoholism is associated with reduced CBF and cerebral metabolism. Sedatives and antianxiety drugs lead to global reduction in CBF and cerebral metabolism. Caffeine, even in small doses, is a potent cerebral vasoconstrictor. Cerebral vasodilation is seen immediately after cigarette smoking, but chronic smokers show global reduction in CBF. Changes in CBF after marijuana smoking are variable; both increases and decreases are seen. Chronic marijuana smoking, however, seems to reduce CBF. Most inhalants and solvents are vasodilators; chronic abuse is accompanied by a decrease in CBF. A number of drugs of abuse, including ethanol, amphetamines, cocaine, nicotine, and caffeine-phenylpropanolamine combinations, increase the risk for stroke. Reduction in CBF associated with chronic use of ethanol, nicotine, inhalants, and solvents is at least partially reversible upon abstinence.

CONCLUSIONS

Topics for future research include regional brain function, which mediates drug-induced mood changes (euphoria); CBF concomitants of psychological and physiological characteristics that increase addiction potential; changes in CBF that accompany withdrawal syndromes; mechanisms responsible for drug-induced stroke; and effects of functional and organic complications on CBF.

Anxiety and cerebral blood flow

The relationship between anxiety and cerebral blood flow (CBF) is of considerable clinical and research significance. Although a considerable amount of information is available on mechanisms through which anxiety may influence CBF, this topic has not received much attention in psychiatry. Earlier techniques for the measurement of CBF were cumbersome and invasive. With the advent of noninvasive techniques, study of CBF in psychiatric disorders, including anxiety, became easier, and a number of such studies have been conducted. In this article the literature on psychophysiological and clinical aspects of changes in CBF associated with anxiety is reviewed.

Behavioral and cerebrovascular effects of caffeine in patients with anxiety disorders

Caffeine is believed to induce anxiety in normal people and anxiety disorder patients and panic attacks in panic disorder patients. The drug is also known to reduce cerebral blood flow (CBF). Findings suggesting an anxiety-related cerebral vasoconstrictive factor have been reported. We examined the relationship between changes in anxiety and CBF induced by intravenously injecting 250 mg of caffeine (comparable to 2 cups of coffee) in 8 patients with generalized anxiety disorder, 9 patients with panic disorder and 9 normal controls. CBF measurements were also obtained before and after an injection of normal saline in another group of 9 normal volunteers. The anxiety disorder patients did not show any evidence of increase in anxiety and panic after caffeine. Both patients and controls who received caffeine but not normal controls who received saline showed significant CBF decrease. The CBF changes were unrelated to changes in mood, autonomic activity and carbon dioxide levels.

Cerebral blood flow responses to inhaled carbon dioxide in schizophrenia

Carbon dioxide (CO2) is a potent cerebrovasodilator; even mild changes in CO2 are associated with marked changes in cerebral blood flow (CBF). We measured CBF before and after 5% CO2 inhalation in 19 medicated patients with schizophrenia and 16 normal volunteers. Another group of 16 volunteers had 2 CBF measurements under resting conditions. Although both patients and controls showed marked CBF increase during CO2 inhalation, the CBF response was significantly less in the patients. Change in CBF per mm of CO2 was lower in the patients. The second group of controls did not show significant differences between the 2 resting CBF measurements.

Chronicity and a low anteroposterior gradient of cerebral blood flow in schizophrenia

Regional cerebral blood flow (CBF) was measured with the 133xenon inhalation technique in 27 patients with schizophrenia of less than 5 years' duration and in 27 patients with schizophrenia of more than 12 years' duration, under resting conditions. Similar measurements were also performed in 54 normal control subjects matched for age and sex. Patients with schizophrenia of long duration had lower anteroposterior gradients of CBF than patients with schizophrenia of short duration and matched control subjects. Covarying out age and end-tidal levels of CO2 did not alter the results.

Hyperfrontality of regional cerebral blood flow distribution in normals during resting wakefulness: fact or artifact?

Earlier studies with two-dimensional measurement techniques consistently found higher frontal flow in normal subjects during resting wakefulness. However, this finding could not be confirmed by several laboratories with the more modern and technologically more sophisticated three-dimensional measurement techniques. This discrepancy can have strong implications for psychiatric research in which both types of techniques are frequently used. This article reviews the existing literature, discusses possible reasons for the discrepancy, and evaluates evidence from other sources on the activity of the frontal lobe during wakefulness.

Responses to hypercarbia induced by acetazolamide in panic disorder patients

CO2 inhalation has been reported to induce panic attacks in panic disorder patients. State anxiety, somatic symptoms of anxiety, physiological changes, and cerebral blood flow (CBF) were monitored in panic disorder patients before and after intravenous injections of 1 g of acetazolamide (13 patients) and saline (10 patients), given under double-blind conditions. In spite of significant hypercarbia, as evidenced by increased CBF in the former group, only one subject reported panic and even that attack did not meet DSM-III-R criteria. There was only one significant difference between the drug and placebo groups; the acetazolamide group experienced significantly more dizziness.

Regional cerebral blood flow changes associated with amyl nitrite inhalation

Regional cerebral blood flow (CBF), mood states and somatic symptoms were measured before and after inhalation of amyl nitrite in 10 physically healthy volunteers with a prior history of using volatile nitrites for recreational purposes. CBF was measured with the same technique, under identical laboratory conditions, in an equal number of normal volunteers. During CBF measurements, blood pressure, pulse rate, respiratory rate and end-tidal levels of carbon dioxide were monitored. The amyl nitrite group and the control group were compared on CBF, rating scale scores and physiological indices via analysis of variance. Amyl nitrite inhalation was associated with significant global increases in CBF, while the control group did not show any change. Pulse rate increase was the only physiological change associated with administration of the drug. Subjects who received the drug reported significant decrease in anger, fatigue and depression and increased palpitation, breathing difficulty, dizziness and headache. Changes in the rating scale scores, physiological indices, and somatic symptoms after amyl nitrite did not correlate with regional CBF change.