Tasks In Normal Subjects Research Articles

Inhibitory Control and the Frontal Eye Fields

Inhibitory control mechanisms are important in a range of behaviors to prevent execution of motor acts which, having been planned, are no longer necessary. Ready examples of this can be seen in a range of sports, such as cricket and baseball, where the choice between execution or inhibition of a bat swing must be made in a brief time interval. The role of the FEFs, an area typically described in relation to eye movement functions but also involved in visual processes, was investigated in an inhibitory control task using transcranial magnetic stimulation (TMS). A stop signal task with manual responses was used, providing measures of impulsivity and inhibitory control. TMS over FEF had no effect on response generation (impulsivity, indexed by go signal RT) but disrupted inhibitory control (indexed by stop signal RT). This is the first demonstration of a role for FEF in this type of task in normal subjects in a task which did not require eye movements and complements previous TMS findings of roles for pre-SMA and inferior frontal gyrus (IFG) in inhibitory control.

Brain Activities on fMRI Using the shiritori Task in Normal Subjects

Shiritori is a popular Japanese word chain game that resembles verbal fluency tasks used in Western countries. Recently, shiritori has been used to determine the dominant hemisphere for language and as a rehabilitation tool. However, there are few reports of neuroimaging during shiritori. We used functional magnetic resonance imaging (fMRI) to conduct a detailed study of brain activities during shiritori and observed activation not only of the left inferior frontal gyrus (including the pars opecularis, the pars triangularis and the pars orbitalis), which is a language-related area, but also of the left superior and middle frontal gyri, the right pars orbitalis (inferior frontal gyrus), and the right cerebellar hemisphere. Shiritori is a useful tool for psychological study and rehabilitation.

Modulation of ongoing cognitive processes by emotionally intense words

Contrary to what occurs with negative pictures, negative words are, in general, not capable of interfering with performance in ongoing cognitive tasks in normal subjects. A probable explanation is the limited arousing power of linguistic material. Especially intense words (insults and compliments), neutral personal adjectives, and pseudowords were presented to 28 participants while they executed a lexical decision task. Insults were associated with the poorest performance in the task and compliments with the best. Amplitude of the late positive component of the event-related potentials, originating at parietal areas, was maximal in response to compliments and insults, but latencies were delayed in response to the latter. Results suggest that intense emotional words modulate ongoing cognitive processes through both bottom-up (attentional capture by insults) and top-down (facilitation of cognitive processing by arousing words) mechanisms.

P31.8 Cortical causality patterns during the execution of a Stroop task in normal subjects by using multimodal integration of high resolution EEG and fMRI recording

P31.8 Cortical causality patterns during the execution of a Stroop task in normal subjects by using multimodal integration of high resolution EEG and fMRI recording

A comparison of label‐based review and ALE meta‐analysis in the Stroop task

Meta-analysis is an important tool for interpreting results of functional neuroimaging studies and is highly influential in predicting and testing new outcomes. Although traditional label-based review can be used to search for agreement across multiple studies, a new function-location meta-analysis technique called activation likelihood estimation (ALE) offers great improvements over conventional methods. In ALE, reported foci are modeled as Gaussian functions and pooled to create a statistical whole-brain image. ALE meta-analysis and the label-based review were used to investigate the Stroop task in normal subjects, a paradigm known for its effect of producing conflict and response inhibition due to subjects' tendency to perform word reading as opposed to color naming. Both methods yielded similar activation patterns that were dominated by response in the anterior cingulate and the inferior frontal gyrus. ALE showed greater involvement of the anterior cingulate as compared to that in the label-based technique; however, this was likely due to the increased spatial level of distinction allowed with the ALE method. With ALE, further analysis of the anterior cingulate revealed evidence for somatotopic mapping within the rostral and caudal cingulate zones, an issue that has been the source of some conflict in previous reviews of the anterior cingulate cortex.

Visual search pattern during the line quadrisection task in normal subjects.

A common test for the assessment of hemispatial neglect is the line bisection test. A recent modification of the task has been reported wherein subjects place a mark at either 25% or 75% of line length ('quadrisection'). In a previous study, we suggested that line quadrisection might entail iteration of two steps involved in standard line bisection: (1) finding the midpoint of the entire line, and then (2) bisecting the half-line segment between the adjudged midpoint and the line end ipsilateral to the target quadrisection point. The present study investigated eye movement patterns during line quadrisection in order to test this hypothesis. Twenty normal volunteers determined the left or right quadrisection point of a horizontal line while their eye movements were recorded using two-dimensional video-oculography. Analysis revealed that, like the results of previous studies on bisection, most normal subjects fixate the central portion of the line segment before reaching the target area during the quadrisection task. Normal subjects' eye movements during quadrisection performance share a number of features with line bisection and provide support for the two-step processing hypothesis.

Silent fMRI Acquisition Methods for Large Acoustic Noise during Scan

Functional magnetic resonance imaging (fMRI) is now the method of choice for studying neural correlates of various tasks in normal subjects as well as patients. This method, however, is inevitably coupled with the acoustic noise produced during the image acquisition process. This is a problem not only in auditory experiments but also in other cognitive tasks in general. The problems caused by such noise are modulation of auditory activation, impaired perception of auditory stimuli, and deterioration of task performance possibly due to stress from the abnormal circumstances. While both hardware and software solutions have been reported, several methods are introduced here that focus on software solutions that can be implemented in scanners already installed. Their advantages and disadvantages differ depending on the kinds of tasks involved, i.e. whether block design or event-related design, and they are discussed with a view to better utilization.

Mechanisms of recovery from aphasia: evidence from positron emission tomography studies

OBJECTIVESLanguage functions comprise a distributed neural system, largely lateralised to the left cerebral hemisphere. Late recovery from aphasia after a focal lesion, other than by behavioural strategies, has been attributed...

Chapter 11 Functional brain imaging and modeling of brain disorders

Publisher Summary This chapter reviews some of the methods that have been used for the analysis of functional brain imaging data. The chapter describes the neural modeling that can be used to provide the basis for understanding the functional networks mediating specific cognitive tasks in normal subjects and in patients with brain disorders. Two types of neural modeling have been applied to functional brain imaging data: systems-level modeling and large-scale neural modeling. The chapter also reviews the use of structural equation modeling. The chapter discusses how large-scale neural modeling can be used to enhance interpretation of functional imaging data. The chapter describes that large-scale neural modeling can help to elucidate complex interactions, such as those that result from recurrent feedforward/feedback loops that are thought to be operative in the brain. With a large-scale model, explicit hypotheses can be examined in different contexts by varying the effects of parameters that correspond to biological substrates, such as synaptic density or receptor efficacy.

Breathing patterns and heart rate during simulated occupational upper limb tasks in normal subjects.

Despite the arms being used extensively in the performance of many occupational tasks, little is known about the pattern of breathing and physiological cost of such work. The purpose of this study was to establish whether a simple change in arm support could alter the workload, pattern of breathing and respiratory muscle recruitment during a low intensity arm task. Ten normal subjects performed a simulated work task when sitting, once with the arms supported and once unsupported. Subjects were required, over a five-minute period, to repeatedly pick up a 2 kg object, inspect and hold it for 15 seconds and then pack it in a box. Breathing pattern responses, measured by pneumotachograph and respiratory inductive plethysmography, were minute ventilation (VE), respiratory frequency (Rf), tidal volume (VT) and change in functional residual capacity (FRC). The main findings were that unsupported arm work was more physiologically demanding than supported arm work. During work VE increased as a result of a change in respiratory frequency but not VT which was much more limited when the arms were unsupported. At the completion of activity, when the arms were unloaded, VT initially increased as VE decreased. FRC and VT were reduced during arm work and increased during recovery, mainly as a result of a change in ribcage excursion. These findings support the theory that during arms activity, intercostal and accessory respiratory muscles act to stabilize the arms and torso, impeding chest wall movement and shifting the respiratory load from these muscles to the diaphragm. This may adversely effect performance of workers who have ventilatory limits to arm work tasks.

Face recognition and postero-inferior hemispheric lesions

Two patients with severe and lasting prosopagnosia were studied for visuo-cognitive functions and anatomo-clinical correlations. Both patients were deficient in recognizing familiar faces and items of previously well known categories (plants and fish for patient 1, mountains for patient 2). Patient 2, but not patient 1, was also deficient for matching of unknown faces. Patient 1, but not patient 2, was achromatopsic. Both patients had bilateral symmetrical lesions. Patient 1 had a lesion of the inferior occipitotemporal cortex, including inferior parts of early stage visual areas. Patient 2 had a lesion of the inferior temporal and fusiform gyri anterior to the early stage visual areas. When compared in Talairach space, the lesions of both patients had minimal overlap. Thus, severe and lasting prosopagnosia was associated with two almost exclusive lesion sites in the postero-inferior part of the hemispheres. Comparison between activation studies of face processing (by others) and our lesion study uncovered several paradoxes. Lesions of regions involved in a given task in normal subjects do not produce a deficit in this task, as shown here for gender discrimination and partially for face matching. Conversely, lesions of a region not specifically involved in a given task in normal subjects can produce a deficit in the task, as shown here for face identification.

Activation of the primary visual cortex by Braille reading in blind subjects.

Primary visual cortex receives visual input from the eyes through the lateral geniculate nuclei, but is not known to receive input from other sensory modalities. Its level of activity, both at rest and during auditory or tactile tasks, is higher in blind subjects than in normal controls, suggesting that it can subserve nonvisual functions; however, a direct effect of non-visual tasks on activation has not been demonstrated. To determine whether the visual cortex receives input from the somatosensory system we used positron emission tomography (PET) to measure activation during tactile discrimination tasks in normal subjects and in Braille readers blinded in early life. Blind subjects showed activation of primary and secondary visual cortical areas during tactile tasks, whereas normal controls showed deactivation. A simple tactile stimulus that did not require discrimination produced no activation of visual areas in either group. Thus in blind subjects, cortical areas normally reserved for vision may be activated by other sensory modalities.

EEG during MR imaging: differentiation of movement artifact from paroxysmal cortical activity.

It is possible to record scalp EEG during the acquisition of gradient-echo/echo-planar MR images or MR spectra without significant degradation of the MR data. [1] Functional MR imaging or spectroscopy with simultaneous EEG recording allows the study of hemodynamic and metabolic changes in vivo in human subjects during cognitive tasks in normal subjects and in patients with paroxysmal epileptiform discharges or ictal events. [2] EEG registration in the MR scanner, however, is very susceptible to a variety of artifacts, particularly patient head movement and ballistocardiogram; the latter is related to head and body movements produced during systole. Despite having the head securely restrained, very small movements of the head produce high-amplitude, paroxysmal bursts on EEG that are impossible to differentiate from paroxysmal cortical epileptiform activity. This artifact results from currents produced by small movements of the EEG electrodes and wires …

Effect of testing procedure on Corsi's block-tapping task in normal subjects and Alzheimer-type dementia.

Corsi's block-tapping task was given to 30 normal subjects and 38 Alzheimer-type demented patients following two different procedures. The first is the most widely standardized (scoring criterion: 3 correct reproductions out of 5 sequences), while the second is more lenient since it does not require subjects to replicate a certain performance three times. Demented patients' scores were lower than those of controls in both conditions, and scores on the two tasks were significantly correlated for patients and controls. However, the requirement of replicating the visuospatial memory performances was more detrimental for demented patients than for controls so the two procedures cannot be considered equivalent.

Voluntary muscle release is not accompanied by H-reflex inhibition in patients with upper moto neuron lesions

Changes in excitability of the soleus (Sol) monosynaptic reflex are were investigated in spastic subjects, affected by amyotrophic lateral sclerosis (ALS), upon voluntary relaxation of tonic contraction of triceps surae muscle. Force and electromyograms (EMG) were recorded during triceps release, performed in response to an acoustic signal, in a reaction-time (RT) situation. Sol H-reflex was evoked at random during the task, and its amplitude was referred in time to the end of Sol EMG. At variance with the results for the same task in normal subjects, it was found that in ALS patients the RTs of the termination of EMG were longer than those of the beginning of the EMG, the decrease in force was prolonged and perturbed owing to intercurrent clonus-like EMG activity, and the H-reflex did not undergo the expected profound inhibition. It is suggested that the absence of the activation of presynaptic inhibitory mechanisms by the descending command to release brings about major disorders in voluntary muscle relaxation.

A noninvasive positron computed tomography technique using oxygen-15--labeled water for the evaluation of neurobehavioral task batteries.

A technique is described that provides information about relative cerebral responses to differing neurobehavioral tasks in normal subjects studied with positron computed tomography and oxygen-15-labeled water. Simulation studies demonstrate that this technique is sensitive to changes in true local CBF within a physiological range and tends to underestimate relative flow changes at high flow values (greater than 30 ml min-1 100 g-1) and to overestimate these changes for flow values of less than 25 ml min-1 100 g-1. Image acquisition times of 60 s following the arrival of oxygen-15-labeled water in the brain were the most accurate for identifying such relative changes between radioisotope administrations and were not limited by statistical noise from total image counts. Studies in normal volunteers indicate that the technique is highly reproducible, demonstrating a coefficient of variation for small (less than 2 cm2) regions of 2.98 between studies in the same state. Visual stimulation studies in normal volunteers demonstrated relative radioisotope concentration changes between control and stimulated states that are in good agreement with similar results obtained using the same stimulation paradigm but with the use of fluorodeoxyglucose to determine cerebral glucose metabolism.

Personality trait and antianxiety drug effects on psychomotor performance

1. 1. Effects of benzodiazepines on the learning of psychomotor tasks in normal subjects with high neuroticism level were examined at the late stage of learning process. 2. 2. Twelve high-neurotic (HN) and 12 low-neurotic (LN) male volunteer subjects received either 5 mg diazepam, 10 mg clobazam or placebo in three treatment conditions using a double-blind method. The treatment order was counter-balanced. 3. 3. Subjects were allowed to practice 9 times on both the choice-reaction-time test (CRTT) and the mirror-drawing test (MDT) before entering the experimental sessions. 4. 4. While under placebo condition there was no difference between HN and LN subjects, HN subjects significantly lowered the CRTT performance than LN subjects under both diazepam and clobazam conditions. 5. 5. Impairment, rather than beneficial, effects of diazepam and clobazam on the CRTT performance were demonstrated in HN subjects.

Hemispheric Laterality Effects on a Facial Recognition Task in Normal Subjects

Comparative recognition accuracies for physiognomic and verbal stimuli were compared when these stimuli were tachistoscopically presented to the left and right visual fields of normal dextral subjects. Results indicated that a majority of the subjects demonstrated a right visual field superiority for the recognition of trigrams, in combination with a left visual field superiority for facial recognition. The introduction of a 10-sec. retention interval in the facial recognition task failed to affect recognition performance appreciably, and it was concluded that the initial perception of the stimuli was relatively more important than their subsequent retention for success on this task. The findings were interpreted within a framework of hemispheric functional asymmetry, and possible topics for future research outlined.

Changes in physiological tremor during repeated performance of a motor task in normal subjects and anxious patients.

It has been found that a significant progressive reduction in the amplitude of physiological tremor in the 4–12 c/sec. range occurs when relatively unpractised subjects carry out a series of trials in a motor task involving a controlled muscle effort (Carrie, in press.