Cerebral lateralization of vigilance: A function of task difficulty

Functional near infrared spectroscopy (fNIRS) measures of cerebral oxygenation levels were collected from participants performing difficult and easy versions of a 12 min vigilance task and for controls who merely watched the displays without a work imperative. For the active participants, the fNIRS measurements in both vigilance tasks showed higher levels of cerebral activity than was present in the case of the no-work controls. In the easier task, greater activation was found in the right than in the left cerebral hemisphere, matching previous results indicating right hemisphere dominance for vigilance. However, for the more difficult task, this laterality difference was not found, instead activation was bilateral. Unilateral hemispheric activation in vigilance may be a result of employing relatively easy/simple tasks, not vigilance per se.     

Feasibility of transcranial Doppler and single photon emission computed tomography in compound neuroactivation task

The aim of this study was to test feasibility of transcranial Doppler (TCD) and single photon emission computed tomography (SPECT) during compound neuroactivation task. The study was performed in 60 healthy right-handed volunteers. Cerebral blood flow velocity was measured by TCD in both middle cerebral arteries (MCA) at baseline and during computer game. The same stimulus and response pattern was used in 15 subjects that additionally underwent brain SPECT. Percentage differences between measurements were determined through quantitative result assessment. Both methods detected a statistically significant cerebral blood flow increase during neuroactivation. Correlation of TCD and SPECT showed statistically significant correlation only for the increase of cerebral blood flow velocity in the right MCA and for the right-sided cerebral blood flow increase, demonstrating that both methods partially measure similar cerebral blood flow changes that occur during neuroactivation. Comparison of TCD and SPECT showed TCD to be inadequately sensitive method for evaluation of cerebral blood flow during complex activation paradigm.     

Caffeine can affect velocity in the middle cerebral artery during hyperventilation, hypoventilation, and thinking: a transcranial Doppler study.

This study examined possible caffeine-mediated changes in blood flow velocity in the middle cerebral artery (VMCA) induced by tests of cerebrovascular responsiveness. Transcranial Doppler (TCD) sonography provided simultaneous bilateral VMCA measures while healthy college students hypoventilated, hyperventilated, and performed cognitive activities (short-term remembering, generating an autobiographical image, solving problems), each in 31-second tests. VMCA measures were obtained from the same persons, in separate testing sessions, when they were noncaffeinated and under two levels of caffeine: a smaller amount (from a cola, 45 mg/12 oz) and a larger amount (from coffee, 117 mg/8 oz). Compared with the no-caffeine control condition, a smaller amount of caffeine had no significant effects on global VMCA, but a larger amount suppressed VMCA by 5.8%. Time-course analyses showed that VMCA (1) followed a triphasic pattern to increase over baselines during hypoventilation regardless of caffeine condition, (2) slowed below baselines during hyperventilation (with the degree of slowing attenuated under caffeine), and (3) increased over baselines during all cognitive activities (ranges 3.8-6.9%). It is concluded that a large amount of caffeine can suppress VMCA, and this possibility should be anticipated when TCD is used to assess cerebral hemovelocity.     

经颅多普勒超声联合体感诱发电位监测在颈动脉内膜剥脱术中的应用价值

目的探讨经颅多普勒超声(TCD)联合体感诱发电位(SEP)监测在颈动脉内膜剥脱(CEA)术中的应用价值。方法对29例颈动脉狭窄患者在CEA术中采用TCD和SEP联合监测,用TCD监测术侧大脑中动脉(MCA)平均血流速度(Vm)的变化,并记录同时段SEP波幅的变化。根据术中TCD和SEP的变化综合判断是否实施转流术,并判断开放颈动脉后有无出现脑血流高灌注。结果本组患者经术中应用TCD和SEP联合监测均顺利完成手术;3例TCD监测MCA Vm及SEP波幅下降均达到转流标准的患者,术中行转流术。SEP(10.3%,3/29)和TCD(44.8%,13/29)监测达到转流标准比率的差异有统计学意义(χ2=4.118,P=0.002)。5例患者TCD监测示术中出现脑血流过度灌注,但此时SEP并无阳性表现,通过适当降血压及压迫颈动脉处理,其中仅1例患者术后出现脑过度灌注综合征。本组患者术后1周内复查CTA或DSA显示颈动脉狭窄均消失。术后随访3~18个月,仅1例患者在术后第10 d出现术侧手功能区小片状脑梗死,其他患者均无出现并发症。结论TCD与SEP联合监测在CEA术中具有较高的临床应用价值;SEP在判断术中是否使用转流方面更有优势,TCD在判断CEA术中高灌注方面有优势。     

Changes in cerebral blood flow induced by passive and active elbow and hand movements

Transcranial Doppler ultrasonography (TCD) has been widely used to obtain information about changes in cerebral perfusion during monitor activity after stroke. This type of application is greatly limited when severe motor deficits are presnet that impede the performance of an active motor task. In this study, we explored the effect of performing passive arm movements on cerebral perfusion. Twenty healthy subjects were investigated. A bilateral TCD monitoring of the middle cerebral artery (MCA) flow velocity was performed during the following experimental conditions: 1-min of active and passive flexion extension elbow movement and 1-min of active and passive dorsal extension hand movement. Each task was performed with both left and right arms. The percentage increase in flow velocity from rest to task performance was calculated. Each task produced a significantly greater increase in mean flow velocity in the contralateral MCA with respect to the ipsilateral. When comparing the effect of passive and active tasks, no significant difference in mean flow velocity changes recorded in the ipsilateral and the contralateral MCA was detected regarding either elbow or hand movements. These findings demonstrate the possibility of obtaining information about changes in hemispheric cerebral perfusion during passive movements involving elbow and hand. This type of application deserves further attention in the study of cerebral functional changes following cerebral lesions. Received: 30 May 2000 / Accepted: 24 July 2000     

Cerebral hemodynamic response induced by the Tower of Hanoi puzzle and the Wisconsin Card Sorting test

Transcranial Doppler sonography (TCD) was applied in normal subjects to investigate the effect of prefrontal functions like the Tower of Hanoi (TOH) task and the Wisconsin Card Sorting test (WCST) on cerebral hemodynamics. In 20 healthy volunteers, left and right middle cerebral artery (MCA) and anterior cerebral artery (ACA) were insonated. The TOH task and the WCST were administered while cerebral blood flow velocity (CBFV) was registered. Each test was repeated once per artery pair. There was a visuomotor test to control the motor and visual stimulations. Three phases of CBFV time course were detected: an initial peak within 5 s, a following decrease within 25 s and a steady state beginning at 40 s. The TOH task, WCST and visuomotor tests had different mean CBFV during the initial peak (MCA: P<0.05; ACA: P<0.05) as well as for the decrease (ACA: P<0.01) and the steady state (MCA: P<0.01; ACA: P<0.01). The TOH showed an increased mean CBFV as compared with the WCST during the steady state (MCA: P<0.01; ACA: P<0.05). However, temporal modulation of mean CBFV during category shift of the WCST resulted in significantly increased values after category shift (MCA: P<0.001; ACA: P<0.01) as compared with CBFV before the category shift. These findings showed a different CBFV pattern during the TOH task and WCST than during the visuomotor test. In conclusion, TCD was able to assess CBFV in prefrontal functions, using a high resolution in time.     

Endothelial apoptosis does not determine symptom status in carotid artery disease

BACKGROUND: Transcranial Doppler sonography (TCD) has been used widely for long-term monitoring of cerebral blood flow without adverse reports. However, attention has not been adequately paid to the fact that an increase in the time period of TCD insonation causes brain temperature to rise due to ultrasound absorption by tissue and the skull. We measured the actual temperature rise in local brain tissue induced by TCD insonation over a long time period during in vivo animal experiments in order to verify whether or not a pause is required in long-term, continuous TCD monitoring. METHODS: We inserted thermocouples into the skull-brain interface (SBI) of 15 New Zealand White rabbits (10: TCD application group; 5: control group, TCD non-application group). The TCD probe was placed on the parietal bone, and changes in SBI temperature (SBIT) were measured for 90 min. TCD was set at maximum output level (0.2 W, 2 MHz). RESULTS: SBIT in the TCD group increased rapidly to 3.47 degrees C within 25 min and then reached a plateau. The maximum time for safe continuous TCD application is estimated to be 33 min. CONCLUSIONS: Even though there are large differences in factors, such as brain volume and environmental conditions, between rabbits and humans, there is less difference in their cerebral blood flow per brain weight, which is the parameter that is mainly associated with heat reduction. Accordingly, the findings of the present experiment suggest that long-term TCD monitoring in clinical use should include a pause after every 30 min of insonation to avoid thermal damage to the brain surface.     

Sustained attention following mild closed-head injury

The sustained-attention performance of patients with mild closed-head injury (CHI) was examined within one month of injury using a high-event rate, digit-discrimination vigilance task with two levels of stimulus degradation (undegraded, highly degraded). Under undegraded stimulus conditions, vigilance performance for mild CHI subjects, uninjured case-matched control subjects, and college students was highly accurate and remained so across the entire task period. When stimuli were presented in degraded fashion, however, all three groups showed a similar decline over time (i.e., vigilance decrement) in hit rates and d' scores. Although mild CHI did not lead to a greater rate of deterioration in vigilance performance in the degraded stimulus condition, it did produce lower overall levels of sensitivity (d') in target detection. These results suggest that, during the first month after mild CHI, vigilance performance is unimpaired under normal task conditions, but may fall short under task conditions that require sustained effortful processing. These findings join a growing body of evidence showing that mild CHI can lead to measurable deficits in cognitive functioning.     

Cerebral blood flow regulation during cognitive tasks: effects of healthy aging

Aging is associated with frontal subcortical microangiopathy and executive cognitive dysfunction, suggesting that elderly individuals may have impaired metabolic activation of cerebral blood flow to the frontal lobes. We used transcranial Doppler (TCD) ultrasound to examine the cerebral blood flow response to executive control and visual tasks in the anterior and posterior cerebral circulations and to determine the effects of healthy aging on cerebral blood flow regulation during cognitive tasks. Continuous simultaneous anterior cerebral artery (ACA) and posterior cerebral artery (PCA) blood flow velocities (BFVs) and mean arterial pressure (MAP) were measured in response to word stem completion (WSC) and a visual search (VS) task in 29 healthy subjects (14 young, 30+/-1.5 years; 15 old, 74+/-1.4 years). We found that: (1) ACA and PCA blood flow velocities are both significantly increased during WSC and VS cognitive tasks, (2) ACA and PCA activations were task specific in our young volunteers, with ACA>PCA BFV during the WSC task and PCA>ACA BFV during the VS task, (3) while healthy elderly subjects also had PCA>ACA BFV during the VS task, they did not have ACA>PCA activation during the WSC task, and (4) healthy elderly subjects tend to have overall greater increases in BFV during both cognitive tasks. We conclude that TCD can be used to monitor cerebrovascular hemodynamics during the performance of cognitive tasks. Our data suggest that there is differential blood flow increase in the ACA and PCA in young versus elderly subjects during cognitive tasks.     

Temporal modulation of cerebral hemodynamics under prefrontal challenge in schizophrenia: a transcranial Doppler sonography study

Transcranial Doppler sonography (TCD) is a non-invasive method to assess cerebral blood flow velocity (CBFV) and hence cerebral blood flow during cognitive activation. Major cognitive dysfunctions have been consistently reported in patients with schizophrenia, and important deficits have been observed with respect to prefrontal functions. However, prefrontal activation in schizophrenics has not been investigated with TCD despite its potential to examine short-term changes of cerebral blood flow. The Wisconsin Card Sorting Test (WCST) and the Tower of Hanoi puzzle were administered to 11 right-handed schizophrenics and 20 healthy controls. The middle and anterior cerebral arteries were pairwise insonated. Schizophrenics showed decreased CBFV during the initial phase of both prefrontal functions and the steady-state phase of the Tower of Hanoi. In healthy controls, there was a succession of three significantly different phases of mean CBFV during the Tower of Hanoi, and there was no such modulation in schizophrenics. Immediately after category shift in the WCST, there was an increase of mean CBFV in healthy controls, but not in schizophrenics. In conclusion, transcranial Doppler sonography was able to detect differing specific alterations of CBFV during two prefrontal tasks in healthy controls and patients with schizophrenia. Importantly, the results of this study imply a degraded pattern of CBFV changes over time in schizophrenia during prefrontal activation.     

Sustained attention following mild closed-head injury

Abstract

The sustained-attention performance of patients with mild closed-head injury (CHI) was examined within one month of injury using a high-event rate, digit-discrimination vigilance task with two levels of stimulus degradation (undegraded, highly degraded). Under undegraded stimulus conditions, vigilance performance for mild CHI subjects, uninjured case-matched control subjects, and college students was highly accurate and remained so across the entire task period. When stimuli were presented in degraded fashion, however, all three groups showed a similar decline over time (i.e., vigilance decrement) in hit rates and d' scores. Although mild CHI did not lead to a greater rate of deterioration in vigilance performance in the degraded stimulus condition, it did produce lower overall levels of sensitivity (d') in target detection. These results suggest that, during the first month after mild CHI, vigilance performance is unimpaired under normal task conditions, but may fall short under task conditions that require sustained effortful processing. These findings join a growing body of evidence showing that mild CHI can lead to measurable deficits in cognitive functioning.     

蛛网膜下腔出血后脑血管痉挛实验研究

目的　在兔蛛网膜下腔出血 (SAH)模型上 ,尝试建立经颅多普勒超声 (TCD)及血管造影 ,监测椎基动脉脑血管痉挛 (CVS)的新方法。方法　兔枕大池一次性注血 ,同时行逆行颈总动脉插管椎基动脉造影及开骨窗TCD监测。结果　逆行性脑血管造影能清晰显示椎基底动脉系统 ,注血前后血管直径差异明显 (P <0 .0 5 ) ,平均血流速度注血后明显增快 ,但中、重度痉挛之间基底动脉血流速度变化无明显差异。结论　一侧颈总动脉逆行插管椎基动脉造影 ,操作简便 ,结果可靠。采取开骨窗以提高TCD超声频率的方法 ,可获得兔基底动脉稳定的频谱图并易于重复。     

Vigilance and fatigue following traumatic brain injury.

Research findings have suggested that individuals with traumatic brain injury (TBI) show greater psychophysiological and subjective costs associated with performing vigilance tasks, but have not examined relationships with fatigue. The present study aimed to investigate vigilance and its relationship with subjective and objective fatigue measures. Forty-six TBI participants and 46 controls completed a 45-minute vigilance task. They also completed a subjective fatigue scale (the VAS-F) and a selective attention task before and after the vigilance task, and had their blood pressure (BP) monitored. TBI participants performed at a lower level on the vigilance task, but performed at a similar level across the duration of the task. Higher subjective fatigue ratings on the VAS-F were associated with more misses on the vigilance task for TBI participants. TBI participants showed greater increases in diastolic BP, and these were associated with greater increases in subjective fatigue ratings on the VAS-F. A subgroup of TBI participants showed a decline in performance on the vigilance task and also showed disproportionate increases in subjective fatigue. Findings provide support for the coping hypothesis, suggesting that TBI individuals expend greater psychophysiological costs in order to maintain stable performance over time, and that these costs are also associated with subjective increases in fatigue.     

Utility of transcranial Doppler ultrasound for the integrative assessment of cerebrovascular function

There is considerable utility in the use of transcranial Doppler ultrasound (TCD) to assess cerebrovascular function. The brain is unique in its high energy and oxygen demand but limited capacity for energy storage that necessitates an effective means of regional blood delivery. The relative low cost, ease-of-use, non-invasiveness, and excellent temporal resolution of TCD make it an ideal tool for the examination of cerebrovascular function in both research and clinical settings. TCD is an efficient tool to access blood velocities within the cerebral vessels, cerebral autoregulation, cerebrovascular reactivity to CO(2), and neurovascular coupling, in both physiological states and in pathological conditions such as stroke and head trauma. In this review, we provide: (1) an overview of TCD methodology with respect to other techniques; (2) a methodological synopsis of the cerebrovascular exam using TCD; (3) an overview of the physiological mechanisms involved in regulation of the cerebral blood flow; (4) the utility of TCD for assessment of cerebrovascular pathology; and (5) recommendations for the assessment of four critical and complimentary aspects of cerebrovascular function: intra-cranial blood flow velocity, cerebral autoregulation, cerebral reactivity, and neurovascular coupling. The integration of these regulatory mechanisms from an integrated systems perspective is discussed, and future research directions are explored.     

Correlation of cerebral hemodynamic changes during mental activity and recovery after stroke

OBJECTIVE: To investigate the correlation between changes in cerebral functional activity during mental engagement and the potential for neurologic recovery after stroke. BACKGROUND: Transcranial Doppler ultrasonography (TCD) makes it possible to detect the dynamic adjustment of cerebral perfusion related to functional neuronal changes. METHODS: TCD monitoring of flow velocity changes in the middle cerebral artery of 29 ischemic stroke patients was performed during an object recognition task. The study took place within 4 weeks from stroke onset. Based on recovery occurring after 2 months, the patients were divided into four groups depending on the side of hemispheric lesion and the presence or absence of neurologic recovery. Ten healthy subjects served as control subjects. RESULTS: During the recognition task, control subjects showed a bilateral increase in flow velocity with respect to the rest phase (right side, 7.02 +/- 1.3%; left side, 6.65 +/- 1. 1%), with no side-to-side difference. In patients who experienced recovery, a similar pattern of bilateral activation was observed, irrespective of the side of the lesion. Conversely, in patients with no recovery, the increase of flow velocity was significantly higher on the side contralateral to the brain lesion (p < 0.0001) with respect to the lesion side. Performance during the recognition task was comparable in the four groups of patients. CONCLUSIONS: These findings suggest that satisfactory recovery from a neurologic deficit requires the persistence of functional activity in the damaged hemisphere despite the presence of an anatomic lesion. The possibility of obtaining early prognostic indications with TCD may be relevant for an early selection of patients with the best probability of benefiting from rehabilitation therapy.     

Cerebral blood flow velocity changes during dichotic listening with directed or divided attention: a transcranial Doppler ultrasonography study.

Simultaneous bilateral transcranial Doppler ultrasonography (TCD) monitoring of blood flow velocity (BFV) in the middle cerebral arteries was performed in 28 normal right-handed volunteers during linguistic dichotic listening tasks to investigate the effect of hemispheric specialisation and allocation of attention. A control task that required the repetition of monaurally presented words was followed by three randomised dichotic listening tasks in which the subjects were instructed to direct their attention to the word stimuli of the right ear, the left ear, or to divide their attention between both ears. Behavioural data indicated that the subjects used the required attentional strategies. A significant right ear advantage was not obtained in the divided attention condition due to a ceiling effect. Each task resulted in a significant bilateral increase in BFV. We found no significant lateralisation of BFV change for any of the tasks. We noted marked differences in BFV change between the different conditions that were significant in the right hemisphere, showed a borderline significance in the left hemisphere and appeared to be related with the difficulty of the task. We conclude that the hemodynamic changes caused by attentional strategies or hemispheric specialisation in processing dichotic stimuli over and above the effect of bilateral auditory stimulation, are too subtle to be detected as lateralised changes in BFV. Functional TCD could be used for the evaluation of a task's workload relative to other tasks, and may contribute to elucidate the role of the right hemisphere in attention and arousal.     

The Effects of Event Rate and Signal Probability on Childrens Vigilance

Using the study of vigilance in adults as their model, the researchers examined task parameters and their interactions in a study of sustained attention in children from a non-clinical population. Two levels of event rate (low and high) were combined with two levels of signal probability (low and high) in 14-minute vigilance tasks in which children viewed small and large squares presented successively on a computer screen. Seven- and eight-year-old children were instructed to press a button whenever a small square appeared. Signal detection analyses were employed, as well as the traditional measures identifying hits, false alarms, and reaction time. The results support the traditional findings in adult tasks: participants performed most accurately and quickly in the high event rate and high probability condition; low probability elicited a more conservative decision-making criterion, a standard characterized by less willingness to risk false alarms; such conservatism increased over the periods of watch; and the vigilance decrement emerged over time. However, the finding that the high event rate condition improved perceptual sensitivity reversed the event rate effect consistently reported in the adult literature. The above findings are discussed in light of both research and clinical implications.     

The effects of event rate and signal probability on children's vigilance

Using the study of vigilance in adults as their model, the researchers examined task parameters and their interactions in a study of sustained attention in children from a non-clinical population. Two levels of event rate (low and high) were combined with two levels of signal probability (low and high) in 14-minute vigilance tasks in which children viewed small and large squares presented successively on a computer screen. Seven- and eight-year-old children were instructed to press a button whenever a small square appeared. Signal detection analyses were employed, as well as the traditional measures identifying hits, false alarms, and reaction time. The results support the traditional findings in adult tasks: participants performed most accurately and quickly in the high event rate and high probability condition; low probability elicited a more conservative decision-making criterion, a standard characterized by less willingness to risk false alarms; such conservatism increased over the periods of watch; and the vigilance decrement emerged over time. However, the finding that the high event rate condition improved perceptual sensitivity reversed the event rate effect consistently reported in the adult literature. The above findings are discussed in light of both research and clinical implications.     

Effects of scopolamine on stimulus sensitivity and response bias in a visual vigilance task

Signal detection analysis was used to examine the effects of scopolamine on a visual vigilance task. A group of non-smokers performed the 60-min task on three separate occasions, receiving a different dose of scopolamine each time. Scopolamine significantly lowered stimulus sensitivity and prevented the rise in response bias which occurred over time in the placebo condition. In a second study methscopolamine was found to have no effect on either stimulus sensitivity or response bias, showing that peripheral cholinergic blockade was not involved in the effects of scopolamine on these measures. It is concluded (1) that in this study central cholinergic blockade disrupted vigilance performance by lowering stimulus sensitivity, and (2) that this finding provides further evidence that central cholinergic pathways are involved in the control of human information processing.     

Cerebral metabolic dysfunction and impaired vigilance in recently abstinent methamphetamine abusers.

BACKGROUND: Methamphetamine (MA) abusers have cognitive deficits, abnormal metabolic activity and structural deficits in limbic and paralimbic cortices, and reduced hippocampal volume. The links between cognitive impairment and these cerebral abnormalities are not established. METHODS: We assessed cerebral glucose metabolism with [F-18]fluorodeoxyglucose positron emission tomography in 17 abstinent (4 to 7 days) methamphetamine users and 16 control subjects performing an auditory vigilance task and obtained structural magnetic resonance brain scans. Regional brain radioactivity served as a marker for relative glucose metabolism. Error rates on the task were related to regional radioactivity and hippocampal morphology. RESULTS: Methamphetamine users had higher error rates than control subjects on the vigilance task. The groups showed different relationships between error rates and relative activity in the anterior and middle cingulate gyrus and the insula. Whereas the MA user group showed negative correlations involving these regions, the control group showed positive correlations involving the cingulate cortex. Across groups, hippocampal metabolic and structural measures were negatively correlated with error rates. CONCLUSIONS: Dysfunction in the cingulate and insular cortices of recently abstinent MA abusers contribute to impaired vigilance and other cognitive functions requiring sustained attention. Hippocampal integrity predicts task performance in methamphetamine users as well as control subjects.