Prefrontal deficits in attention and inhibitory control with aging

Event-related potentials and behavioral measures were obtained from young and elderly subjects while they performed two different auditory delayed match-to-sample tasks. In each experiment, subjects had to indicate whether an initial and a subsequent test sound were identical in two different conditions: one filled with distracting tone pips and one with no distractors. Electrophysiologically, elderly subjects had reduced attention-related activity over frontal regions. In addition, the distracting stimuli elicited an enhanced primary auditory evoked response in the elderly. The percentage of perseverative errors on the Wisconsin card sorting test, a putative measure of frontal lobe function, was positively correlated with the amplitude of the primary auditory evoked response in elderly subjects. Behaviorally, elderly subjects were impaired by distractors at long but not short delays. Taken together, these results suggest that increased distractibility and impaired sustained attention with aging may be due to altered prefrontal cortex function. These data support the loss of prefrontal suppression over the primary auditory regions with aging.      

Differential effects of 6-OHDA lesions of the frontal cortex and caudate nucleus on the ability to acquire an attentional set

Evidence from both human and animal studies indicates that catecholamine (dopamine and noradrenaline) imbalances in the fronto-striatal circuitry are associated with deficits in higher- order cognitive functions. The present study examined how catecholamines within this circuitry modulate attentional function, specifically the ability to develop, maintain, and shift an attentional set. Catecholamine depletions within the frontal cortex of the common marmoset impaired the ability to acquire an attentional set, and increased susceptibility to distraction from task-irrelevant stimuli. Analysis of set-shifting performance with stimulus dimensions of varying salience suggested that frontal catecholamine depletion selectively disrupts "top-down", but not "bottom-up" attentional processing. In contrast, the ability to acquire and shift an attentional set remained intact following dopaminergic depletion from the caudate nucleus. However, the reduced susceptibility to distraction from task-irrelevant stimuli displayed by monkeys with dopaminergic depletions of the caudate nucleus suggests that responding was under more rigid control by the currently rewarded stimulus. The results demonstrate opposite behavioural effects of 6-hydroxydopamine (6-OHDA) lesions in the frontal cortex and caudate nucleus in tasks requiring selective attention. Frontal catecholamine depletion caused an increase in distractibility while caudate dopamine loss induced greater focusing of responding.     

Neural system for controlling the contents of object working memory in humans

Working memory (WM), the active maintenance of currently relevant information, is a flexible system allowing for fast and frequent goal-directed changes of rehearsed information. Successful WM maintenance prevents interference from distracting stimuli while allowing new task-relevant information to update the contents of WM. We used functional magnetic resonance imaging to show that when WM contents were updated, regardless of stimulus type (faces or houses), a frontoparietal network showed transient increases in activation. Some of these regions are highly similar to those identified in studies of shifting attention, supporting the idea that updating WM involves a change in the attentional priority afforded to the current perceptual input. A region within the mid-ventrolateral prefrontal cortex, near the junction of the inferior frontal sulcus and precentral sulcus (inferior frontal junction), that has previously been implicated in cognitive control, demonstrated transient increases in activity during updating as well as sustained maintenance activity. A more anterior prefrontal region, middle frontal gyrus, previously implicated in protecting the contents of WM from interfering stimuli during maintenance, demonstrated transient increases in activity during updating. The current study suggests that updating WM results from a combination of increased attention to the visual stimulus and a change in the system's interference protection state.     

Brain activity related to working memory and distraction in children and adults

In order to retain information in working memory (WM) during a delay, distracting stimuli must be ignored. This important ability improves during childhood, but the neural basis for this development is not known. We measured brain activity with functional magnetic resonance imaging in adults and 13-year-old children. Data were analyzed with an event-related design to isolate activity during cue, delay, distraction, and response selection. Adults were more accurate and less distractible than children. Activity in the middle frontal gyrus and intraparietal cortex was stronger in adults than in children during the delay, when information was maintained in WM. Distraction during the delay evoked activation in parietal and occipital cortices in both adults and children. However, distraction activated frontal cortex only in children. The larger frontal activation in response to distracters presented during the delay may explain why children are more susceptible to interfering stimuli.     

Increased inattentional blindness in severe traumatic brain injury: evidence for reduced distractibility?

Primary objective: To examine the role of selective attention and visual perception in medicating inattentional blindness in a severe traumatic brain injured sample.

Research design: Cross-sectional design with age and education matched control sample.

Methods and procedures: Twenty participants with severe traumatic brain injury (n = 10) and matched controls (n = 10) completed a series of tests of focused attention (Stroop test), divided attention (Trail Making Test), visual perception (Visual Object and Space Perception Battery) and two tasks of inattentional blindness.

Main outcomes and results: The group with severe TBI were significantly slower on the Stroop test and TMT and displayed significantly elevated Stroop interference and TMT ratio scores. On the inattentional blindness tasks, fewer TBI participants identified a distracting stimulus.

Conclusion: The results indicate severe TBI is associated with deficits to focused and divided attention with the finding of a potentially more debilitating impairment arising from reduced distractibility following severe TBI.     

减阻牵张快速牙移动不同加力方式下骨改建效果观察

目的：观察不同牵张力下减阻牵张快速移动牙牙周组织骨改建情况。方法：Beagle犬12只,随机分为加力5天、15天、加力15天固定保持10天、90天组共四组,拔除犬双侧下颌第二前磨牙,选择下颌第一前磨牙为移动牙。将每组6颗牙齿随机分配为减阻-牵张方法组、减阻-常规方法组和常规方法组,每组2颗牙。按相应分组定期取材并制作切片,行HE、MASSON三色染色并观察。结果：减阻牵张方法组第一前磨牙远中移动量远大于减阻常规方法组和常规方法组（P〈0．05）,且3组支抗牙前移量无显著差异（P〉0．05）;组织学观察减阻牵张组张力侧成骨最为活跃,且未见牙周膜结构破坏,而压力侧少见透明样变组织。MASSON染色观察减阻牵张组新生骨较其余两组更为明显,长期保持后骨质良好。结论：减阻牵张方法能有效激发正畸移动牙牙周组织骨改建,且无不良反应,适宜强牵张力是实现牙齿快速移动的必要条件。     

Increased action potential firing rates of layer 2/3 pyramidal cells in the prefrontal cortex are significantly related to cognitive performance in aged monkeys

The neurobiological substrates of significant age-related deficits in higher cognitive abilities mediated by the prefrontal cortex (PFC) are unknown. To address this issue, whole-cell current-clamp recordings were used to compare the intrinsic membrane and action potential (AP) firing properties of layer 2/3 pyramidal cells in PFC slices from young and aged behaviorally characterized rhesus monkeys. Most aged subjects demonstrated impaired performance in Delayed Non-Match to Sample (DNMS) task acquisition, DNMS 2 min delay and the Delayed Recognition Span task. Resting membrane potential and membrane time constant did not differ in aged relative to young cells, but input resistance was significantly greater in aged cells. Single APs did not differ in terms of threshold, duration or rise time, but their amplitude and fall time were significantly decreased in aged cells. Repetitive AP firing rates were significantly increased in aged cells. Within the aged group, there was a U-shaped quadratic relationship between firing rate and performance on each behavioral task. Subjects who displayed either low or very high firing rates exhibited poor performance, while those who displayed intermediate firing rates exhibited relatively good performance. These data indicate that an increase in AP firing rate may be responsible, in part, for age-related PFC dysfunction.     

Impaired filtering of distracter stimuli by TE neurons following V4 and TEO lesions in macaques

Directing attention to a behaviorally relevant visual stimulus can overcome the distracting effects of other nearby stimuli. Correspondingly, physiological studies indicate that attention serves to filter distracting stimuli from receptive fields (RFs) in several extrastriate areas. Moreover, a recent study demonstrated that lesions of extrastriate areas V4 and TEO produce impairments in attentional filtering. A critical remaining question concerns why lesions of ventral stream areas cause attentional filtering impairments. To address this question, we tested the effects of restricted area V4 and TEO lesions on both behavioral performance and the responses of downstream neurons in area TE. The lesions impaired behavioral discrimination thresholds and altered neuronal selectivity for target stimuli in the presence of distracters. With attention to the target, but in the absence of V4 and/or TEO inputs, TE neurons responded as though attentional inputs could no longer be used to filter distracters from their RFs. This presumably occurred because top-down attentional signals were no longer able to filter distracters from the RFs of the cells that provide TE with major input. Consistent with this interpretation, increasing the spatial separation between targets and distracters, such that they no longer fell within a typical V4 RF dimension, restored both behavioral performance and neuronal selectivity in the portion of TE RFs affected by the V4 lesion.     

Distraction in the operating room: A narrative review of environmental and self-initiated distractions and their effect on anesthesia providers

The operating room (OR) is a busy environment with multiple opportunities for distraction. A well-trained anesthesiologist or certified registered nurse anesthetist (CRNA) should remain focused on providing excellent patient care despite these potential distractions. The purpose of this narrative review is to present the multiple types of OR distractions and evaluate each for their level of distraction and their likely impact on patient safety. Distractions in the OR are common and numerous types of distractions exist. Loud OR background noise can lead to miscommunication within the OR team. In several studies, OR noise has been shown to decrease vigilance and possibly delay recognition of non-routine events. The most commonly observed distracting events are “small talk” and staff entering and exiting the OR and most intense distracting events are faulty or unavailable equipment. Phone and pager use can be particularly distracting. Self-initiated distractions can be seen as unprofessional and can negatively impact patient safety. The impact of OR distractions on patient outcomes deserves more vigorous investigation. We must provide anesthesia trainees with the skills to remain vigilant despite numerous and varied OR distractions while also attempting to reduce such OR distractions to improve patient safety. Further research is needed to inform the institution of policies to lessen unnecessary OR distractions.     

Converging neuronal activity in inferior temporal cortex during the classification of morphed stimuli

How does the brain dynamically convert incoming sensory data into a representation useful for classification? Neurons in inferior temporal (IT) cortex are selective for complex visual stimuli, but their response dynamics during perceptual classification is not well understood. We studied IT dynamics in monkeys performing a classification task. The monkeys were shown visual stimuli that were morphed (interpolated) between pairs of familiar images. Their ability to classify the morphed images depended systematically on the degree of morph. IT neurons were selected that responded more strongly to one of the 2 familiar images (the effective image). The responses tended to peak approximately 120 ms following stimulus onset with an amplitude that depended almost linearly on the degree of morph. The responses then declined, but remained above baseline for several hundred ms. This sustained component remained linearly dependent on morph level for stimuli more similar to the ineffective image but progressively converged to a single response profile, independent of morph level, for stimuli more similar to the effective image. Thus, these neurons represented the dynamic conversion of graded sensory information into a task-relevant classification. Computational models suggest that these dynamics could be produced by attractor states and firing rate adaptation within the population of IT neurons.     

Dissociation of stimulus relevance and saliency factors during shifts of visuospatial attention

The control of visuospatial attention entails multiple processes, including both voluntary (endogenous) factors and stimulus-driven (exogenous) factors. Exogenous processes can be triggered by visual targets presented at a previously unattended location, thus capturing attention in a stimulus-driven manner. However, little is known about the relative role of stimulus salience and behavioral relevance for this type of spatial reorienting. Here, we directly assessed how salience and relevance affect activation of the frontoparietal attentional system, using either low-salience but task-relevant target stimuli or salient but task-irrelevant flickering checkerboards. We compared event-related functional magnetic resonance imaging responses for stimuli presented at the unattended versus attended side (invalid minus valid trials), separately for the 2 categories of visual stimuli. We found that task-relevant invalid targets activated the frontoparietal attentional network, demonstrating that this system engages when target stimuli are presented at an unattended location, even when these have a low perceptual salience. Conversely, the presentation of high-salience checkerboards in one hemifield while endogenous attention was engaged elsewhere did not activate the attentional network. These findings indicate that task relevance is critical for stimulus-driven engagement of the attentional network when attentional resources are endogenously allocated somewhere else.     

Compelled Attention: The Effects of Viewing Trauma-Related Stimuli on Concurrent Task Performance in Posttraumatic Stress Disorder

We examined the ability of Vietnam veterans with PTSD to focus attention on a primary digit detection task while concurrently viewing neutral or Vietnam-related picture and word distractors. Controlling for combat exposure, military service, and psychopathology, veterans with PTSD took longer to detect the target when Vietnam-related pictures were distractors. There were no reaction time differences when word stimuli were distractors. The latency effect was specific to trials with trauma-related pictures and did not spread to neutral trials interleaved within a mixed block of trauma and neutral pictures. Individuals with PTSD recalled proportionally more Vietnam-related words than other groups, implying differential attention to Vietnam-related words. Attending to trauma-related pictures interferes with performance of a concurrent task by individuals with PTSD.     

Distinct gamma-band components reflect the short-term memory maintenance of different sound lateralization angles

Oscillatory activity in human electro- or magnetoencephalogram has been related to cortical stimulus representations and their modulation by cognitive processes. Whereas previous work has focused on gamma-band activity (GBA) during attention or maintenance of representations, there is little evidence for GBA reflecting individual stimulus representations. The present study aimed at identifying stimulus-specific GBA components during auditory spatial short-term memory. A total of 28 adults were assigned to 1 of 2 groups who were presented with only right- or left-lateralized sounds, respectively. In each group, 2 sample stimuli were used which differed in their lateralization angles (15 degrees or 45 degrees) with respect to the midsagittal plane. Statistical probability mapping served to identify spectral amplitude differences between 15 degrees versus 45 degrees stimuli. Distinct GBA components were found for each sample stimulus in different sensors over parieto-occipital cortex contralateral to the side of stimulation peaking during the middle 200-300 ms of the delay phase. The differentiation between "preferred" and "nonpreferred" stimuli during the final 100 ms of the delay phase correlated with task performance. These findings suggest that the observed GBA components reflect the activity of distinct networks tuned to spatial sound features which contribute to the maintenance of task-relevant information in short-term memory.     

Effects of phenobarbital on cerebral blood flow and metabolism in young and aged rats

The cerebrovascular and cerebral metabolic changes produced by intraperitoneal injection of phenobarbital (50, 150, and 250 mg/kg) were studied in young adult (6-month) and senescent (28-month) Wistar rats. Cerebral blood flow (CBF) was measured using radioactive microspheres and cerebral oxygen consumption (CMRO2) was obtained by multiplying cortex CBF by the arterial-sagittal sinus oxygen content difference. Control values for blood pressure, blood gas tensions, CBF, and CMRO2 were similar in the young and aged animals during 70% N2O/30% O2. Intraperitoneal phenobarbital produced dose-dependent decreases in CBF with no significant difference between young and aged rats at each phenobarbital dose. At the highest phenobarbital dose (250 mg/kg) CBF was reduced by 49% in the young rats and 52% in the aged rats (P greater than 0.10). CMRO2 was also depressed in a dose-dependent fashion in both young and aged animals with each phenobarbital dose. However, the decrease produced by the highest phenobarbital dose was significantly greater in the aged rats (55%) than the young rats (43%, P less than 0.05), even though the EEG was isoelectric in both groups. The difference in CMRO2 between young versus aged rats at a time when the EEG is isoelectric suggests that high-dose phenobarbital may depress nonelectrical cerebral metabolic processes more in aged rats.     

Percutaneous Reduction and Fixation of Intraarticular Calcaneal Fractures

OBJECTIVE: Percutaneous reduction by distraction and subsequent percutaneous screw fixation to restore calcaneal and posterior talocalcaneal facet anatomy. The aim of this technique is to improve functional outcome and to diminish the rate of secondary posttraumatic arthrosis compared to conservative treatment and, secondly, to reduce infectious complications compared to open reduction and internal fixation (ORIF). INDICATIONS: Sanders type II-IV displaced intraarticular calcaneal fractures. CONTRAINDICATIONS: Isolated centrally depressed fragment. Patients who are expected to be noncompliant. SURGICAL TECHNIQUE: Four distractors (Synthes) are positioned, two on each side of the foot, between the tuberosity of the calcaneus and talus and between the tuberosity and cuboid. A distracting force is given over all four distractors. A blunt drifter is then introduced from the plantar side to unlock and push up any remaining depressed parts of the subtalar joint surface of the calcaneus. The reduction is fixated with two or three screws inserted percutaneously. POSTOPERATIVE MANAGEMENT: Directly postoperatively, full active range of motion exercises of the ankle joint can start, with the foot elevated in the 1st postoperative week. Stitches are removed after 14 days. Implant removal is necessary in 50-60% of patients. RESULTS: Between 1999 and 2004, 59 patients with 71 fractures were treated by percutaneous skeletal triangular distraction and percutaneous fixation. A total of 50 patients with 61 fractures and a minimum follow-up of 1 year were available for follow-up. According to the American Orthopaedic Foot and Ankle Society Hindfoot Score, 72% had a good to excellent result. A secondary subtalar arthrodesis was performed in five patients and planned in four (total 15%). B?hler's angle increased by about 20 degrees postoperatively. Sagittal motion was 90% and subtalar motion 70% compared to the healthy foot.     

Selective output-discriminative signals in the motor cortex of waking monkeys.

Monkeys and humans have similar capacities to discriminate between the frequencies of mechanical sinusoids delivered to the glabrous skin of their hands. Combined psychophysical-electrophysiological experiments in monkeys discriminating in the range of flutter provided evidence that this capacity depends upon differences in the cycle lengths in the sets of periodically entrained activity, evoked by the stimuli discriminated, in neurons of areas 3b and 1 of the (sensory) hemisphere opposite the stimulated hand. Identical experiments have now been made, in similarly trained and discriminating monkeys, in the motor cortex (area 4) of the hemisphere opposite the arm projecting selectively to one of two targets, to indicate discrimination (five hemispheres, 1137 neurons studied). We observed a selective signal of the upcoming correct discrimination in about 25% of the neurons of area 4 active in the task. The neuronal discharge occurs selectively for stimuli either lower or higher in frequency than that of the base stimulus, and commonly begins within 200-300 msec after onset of the comparison stimulus. These neuronal discharges are aperiodic, with no sign of the stimulus frequencies. EMG recording during performance of the discrimination showed that the muscles of the arm opposite the side of recording were silent during the period of stimulus presentations. Recordings during trials in which the animal made errors showed most commonly that the output of the discrimination operation was itself in error, followed by an appropriate arm projection to the wrong target. We interpret the selective response during the comparison stimulus to be a postdiscrimination signal projected transcallosally from the sensory hemisphere to the motor area of the hemisphere controlling the responding arm. We obtained no evidence that the discrimination operation is localized to any particular area, and we surmise it to occur in the dynamic activity within the distributed system linking the sensory cortex of one hemisphere and the motor cortex of the other. One-third of the neurons of the motor cortex responded to indentation of the skin of the ipsilateral hand, at trial onset. These responses varied from those closely linked to that sensory stimulus to those linked to the upcoming movement of the contralateral hand. These onset responses did not occur when similar sequences of mechanical stimuli were delivered to alert but idling monkeys.     

The effects of stimulus modality and frequency of stimulus presentation on cross-modal distraction

Selective attention produces enhanced activity (attention-related modulations [ARMs]) in cortical regions corresponding to the attended modality and suppressed activity in cortical regions corresponding to the ignored modality. However, effects of behavioral context (e.g., temporal vs. spatial tasks) and basic stimulus properties (i.e., stimulus frequency) on ARMs are not fully understood. The current study used functional magnetic resonance imaging to investigate selectively attending and responding to either a visual or auditory metronome in the presence of asynchronous cross-modal distractors of 3 different frequencies (0.5, 1, and 2 Hz). Attending to auditory information while ignoring visual distractors was generally more efficient (i.e., required coordination of a smaller network) and less effortful (i.e., decreased interference and presence of ARMs) than attending to visual information while ignoring auditory distractors. However, these effects were modulated by stimulus frequency, as attempting to ignore auditory information resulted in the obligatory recruitment of auditory cortical areas during infrequent (0.5 Hz) stimulation. Robust ARMs were observed in both visual and auditory cortical areas at higher frequencies (2 Hz), indicating that participants effectively allocated attention to more rapidly presented targets. In summary, results provide neuroanatomical correlates for the dominance of the auditory modality in behavioral contexts that are highly dependent on temporal processing.     

Cord/spine motion in experimental spinal cord injury

We examined cord motion and cord-spine coupling associated with the axial tension and dorsal impact models of spinal cord injury. In 20 cats, distraction forces up to 15 kg were applied. Five microliters of radiopaque agent was injected into the central cord at C4-C7 (14 cats) and T6-L1 (6 cats) at 2-mm intervals. In 20 cats, 300 g/cm impacts were delivered after injection of contrast at 2-mm intervals from the impact point. Trials were conducted under fluoroscopy. At 5-kg distraction, vertebral motion averaged 2.12 mm and cord motion averaged 1.03 mm (coupling ratio = .49). At 10-kg coupling increased to .75. Between 10 and 15-kg distraction, the amount of increase in cord length slowed, as did the ratio (.59). Differences in length between load groups were significant at most levels, and motion corresponded with histologic injury reported previously. In the thoracolumbar region, minimal spine motion and no cord motion occurred. Spine motion was not seen with dorsal impact although cord motion at 2 mm from impact averaged 1.3 mm/300 g/cm, which decreased away from the impact point. The spinal cord has limited elasticity, which may be related to injury. Because spine and cord motion occur in clinical injury, experimental models need to incorporate this element.     

Dynamic cardiocirculatory control during propofol anesthesia in mechanically ventilated patients

We evaluated dynamic cardiovascular control by spectral analytical methods in 20 young adults anesthetized with propofol (2.5 mg/kg, followed by continuous infusion of 0.1 mg/kg/min) and in an awake control group during cyclic stimulation of the carotid baroreceptors via sinusoidal neck suction at 0.2 Hz (baroreflex response mediated mainly by vagal activity) and at 0.1 Hz (baroreflex response mediated by vagal and sympathetic activity). During anesthesia and mechanical ventilation at 0.25 Hz, major underdampened hemodynamic oscillations occurred at 0.055 +/- 0.012 Hz. The response of RR intervals to baroreceptor stimulation at 0.2 Hz was markedly decreased during anesthesia (median of transfer function magnitude between neck suction and RR intervals 3% of the awake control). Blood pressure response to baroreceptor stimulation at 0.1 Hz was significantly decreased during anesthesia to 26% (systolic blood pressure), and 44% (diastolic blood pressure) of the awake control. There was a significant delay in baroreflex effector responses during anesthesia. Our results demonstrate a markedly depressed vagally mediated heart rate response and an impaired blood pressure response to cyclic baroreceptor stimulation during propofol anesthesia in mechanically ventilated patients. The disturbed baroreflex control is accompanied by an irregular dynamic behavior of cardiovascular regulation, indicating a decreased stability of the control system. Implications: An irregular dynamic behavior of the cardiovascular control system, associated with an impaired baroreflex control of heart rate and blood pressure, can be observed during propofol anesthesia in mechanically ventilated subjects.     

How, when, and why to predict IDDM

Insulin-dependent diabetes remains a serious disease replete with life-threatening complications. The onset of the disease is becoming increasingly predictable through the detection of its associated autoantibodies. The natural history of pathogenic events is attenuated in those with adult onset over that seen in infants and children. Immunosuppression therapies in newly diagnosed patients have been shown to induce remissions, whereas various intervention strategies in rodent models (BB rats and nonobese diabetic mice) can delay and even prevent the onset of diabetes. The stage is set for serious consideration of intervention trials to delay the clinical disease in humans.