Ruptured pericallosal aneurysm causing hemorrhage along the fornix.

We present a 57 year-old man with a pericallosal aneurysm causing parenchymal hemorrhage in the preseptal region of the frontal lobe with extension into the fornix. We briefly discuss the literature pertaining to ruptured pericallosal aneurysms and their bleeding patterns.

Determination of cerebral hemisphere language dominance with functional magnetic resonance imaging.

Functional MR imaging (fMRI) is useful for the determination of cerebral hemisphere language dominance, but it can be misleading if the imaging studies are not performed properly. The theoretic and technical problems involved in this use of fMRI are discussed, including behavioral paradigms, data analysis methods, subject handedness, and gender.

Temporal lobe activation demonstrates sex-based differences during passive listening.

PURPOSE: To evaluate potential sex differences in temporal lobe activation during the performance of a functional magnetic resonance (MR) imaging passive-listening paradigm. MATERIALS AND METHODS: Twenty strongly right-handed volunteers (10 men, 10 women) underwent imaging with a 1.5-T machine by using a gradient-echo echo-planar sequence. The task consisted of passive listening to simple narrative text interleaved with same-narrative text played backward. Volumes of interest were drawn around anterior and posterior areas of activation in bilateral temporal lobes. The peak percentage of activation and the percentage of activated voxels at single-voxel significance levels of 10(-2), 10(-3), and 10(-4) within each volume of interest were measured. An asymmetry index A was then calculated for both anterior and posterior volumes of interest such that A = (L - R)/(L + R), where R is either the peak percentage activation or the percentage of activated voxels within the right volume of interest and L is either the peak percentage activation or the percentage of activated voxels within the left volume of interest. The asymmetry indexes were compared between men and women by using a standard t test. RESULTS: Men showed a significantly higher degree of asymmetric activation than did women in both the anterior and posterior volumes of interest by using peak percentage activation and at all single-voxel significance levels. The degree of activation asymmetry was greater by using single-voxel significance measurements, compared with peak percentage activation measures. CONCLUSION: Women demonstrate a higher degree of bilateral language representation in temporal lobe regions than do men during passive listening. These findings, combined with the variable results of prior functional MR imaging language studies of sex differences, suggest that they may be task specific.

Correlations in low-frequency BOLD fluctuations reflect cortico-cortical connections.

Cross-correlation of low-frequency temporal fluctuations (<0.08 Hz) was used to correlate widely separated anatomic regions during continuous performance of a spatial working memory task. The regions of highest correlation to right-hemisphere dorsolateral prefrontal cortex correspond to the regions of largest baseline signal change in a conventional block-style functional MRI paradigm. Additionally, it is shown that the correlations between elements of the functional network increase during performance of a task that activates the network when compared to a task that does not directly stimulate the functionally connected network.

Quantitative comparison of functional contrast from BOLD-weighted spin-echo and gradient-echo echoplanar imaging at 1.5 Tesla and H2 15O PET in the whole brain.

Spin-echo and gradient-echo echoplanar functional magnetic resonance imaging (fMRI) studies at 1.5 Tesla (T) were used to obtain blood oxygenation level-dependent (BOLD) contrast images of the whole brain in seven strongly right-handed women during execution of a complex motor task. Five subjects underwent subsequent H215O positron emission tomography (PET) studies while performing the same task. Group-averaged results for changes in the MRI relaxation rates R2* and R2 at 1.5T in response to neuronal activation in nine cortical, subcortical, and cerebellar motor regions are reported. Results for each method are grouped according to tissue type-cerebral cortex (precentral gyrus and supplementary motor area), subcortical regions (thalamus and putamen), and cerebellar cortex (superior lobule). The observed changes in R2* from activation-induced oxygenation changes were more variable across brain regions with different tissue characteristics than observed changes in R2. The ratio of deltaR2* to deltaR2 was 3.3 +/- 0.9 for cerebral cortex and 2.0 +/- 0.6 for subcortical tissue. deltaR2*, deltaR2, and relative blood flow changes were deltaR2* = -0.201 +/- 0.040 (s-1), deltaR2 = -0.064 +/- 0.011 s(-1), and deltaf/f = 16.7 +/- 0.8% in the cerebral cortex; deltaR2* = -0.100 +/- 0.026 s(-1), deltaR2 = -0.049 +/- 0.009 s(-1), and deltaf/f = 9.4 +/- 0.7% in the subcortical regions; and deltaR2* = -0.215 +/- 0.093 s(-1), deltaR2 = -0.069 +/- 0.012 s(-1), and deltaf/f = 16.2 +/- 1.2% in the cerebellar cortex.

Comparison of rhyming and word generation with FMRI.

Functional magnetic resonance imaging (FMRI) has been successfully used to non-invasively map language function, but has several disadvantages. These include severe motion sensitivity, which limits overt verbal responses in behavioral paradigms, such as word generation. The lack of overt responses prevents behavioral validation, making data interpretation difficult. Our objective was to compare the FMRI activation patterns of a novel silent rhyme determination task requiring a non-verbal response, to covert word generation from visually presented letters. Five strongly right-handed subjects performed both tasks during multi-slice coronal echo-planar T2*-weighted FMRI. Single subject activation maps were generated for each task by correlation analysis of single pixel time series to a boxcar reference function. These maps for the two tasks were separately interpolated to 256(3), transformed into Talairach space, summed, and thresholded at t>6. Combined activation maps from both tasks showed similar robust perisylvian language area activation, including inferior frontal gyrus, posterior superior temporal lobe, and fusiform gyrus. Subjects performed well on the rhyming task, which activated left hemisphere cortical regions more selectively than the word generation task. The rhyming task showed less activation than the word generation task in areas typically not considered specifically related to language function, such as the dorsolateral prefrontal cortex and anterior cingulate. The rhyming task is a useful tool for brain mapping and clinical applications, potentially more specific to cortical language areas than verbal fluency.

Comparison of fMRI and intraoperative direct cortical stimulation in localization of receptive language areas.

PURPOSE: The purpose of this work was to compare the cortical localization of receptive speech using functional MRI (fMRI) and direct intraoperative electrical stimulation. METHOD: Three strongly right-handed patients with primary neoplasms of the left parasylvian region underwent fMRI while subjected to a passive listening task designed to activate receptive language areas. All three subjects then underwent awake intraoperative language mapping using direct electrical stimulation of the cortex. RESULTS: In all three subjects, similar, but nonidentical, cortical regions were identified as involved in receptive language function by fMRI and direct cortical stimulation mapping. CONCLUSION: fMRI provides excellent receptive language mapping, but its results must be interpreted with caution due to conceptual and technical differences from direct cortical stimulation mapping.

Motor cortical activity preceding a memorized movement trajectory with an orthogonal bend.

Two monkeys were trained to make an arm movement with an orthogonal bend, first up and then to the left ([symbol: see text]), following a waiting period. They held a two-dimensional manipulandum over a spot of light at the center of a planar working surface. When this light went off, the animals were required to hold the manipulandum there for 600-700 ms and then move the handle up and to the left to receive a liquid reward. There were no external signals concerning the "go" time or the trajectory of the movement. It was hypothesized that during that period signs of directional processing relating to the upcoming movement would be identified in the motor cortex. Following 20 trials of the memorized movement trajectory, 40 trials of visually triggered movements in radially arranged directions were performed. The activity of 137 single cells in the motor cortex was recorded extracellularly during performance of the task. It was found that 62.8% of the cells changed activity during the memorized waiting period. During the waiting period, the population vector (Georgopoulos et al. 1983, 1984) began to grow approximately 130 ms after the center light was turned off; it pointed first in the direction of the second part of the memorized movement (<--) and then rotated clockwise towards the direction of the initial part of the movement (increases). These findings indicate processing of directional information during the waiting period preceding the memorized movement. This conclusion was supported by the results of experiments in ten human subjects, who performed the same memorized movement ([symbol: see text]). In 10% of the trials a visual stimulus was shown in radially arranged directions in which the subjects had to move; this stimulus was shown at 0, 200, and 400 ms from the time the center light was turned off. We found that as the interval increased the reaction time shortened for the visual stimulus that was in the same direction as the upward component of the memorized movement.

Three-dimensional drawings in isometric conditions: planar segmentation of force trajectory.

Normal human subjects grasped an isometric handle with an unrestrained, pronated hand. They were asked to exert forces continuously to draw lemniscates (figure eights) in specified or self-chosen planes and in the presence or absence of a three-dimensional visual feedback cursor and a visual template. In every condition, the mean plane orientation in the force space differed appreciably between the two loops of the figure, as described previously by Soechting and Terzuolo (1987a) for free drawing arm movements. These findings suggest that the planar segmentation of the motor trajectory is not a consequence of joint motion but arises from central constraints related to the production of motor trajectory in space.

Three-dimensional drawings in isometric conditions: relation between geometry and kinematics.

Normal human subjects grasped a 3-D isometric handle with an otherwise unrestrained, pronated hand and exerted forces continuously to draw circles, ellipses and lemniscates (figure-eights) in specified planes in the presence or absence of a 3-D visual force-feedback cursor and a visual template. Under any of these conditions and in all subjects, a significant positive correlation was observed between the instantaneous curvature and angular velocity, and between the instantaneous radius of curvature and tangential velocity; that is, when the force trajectory was most curved, the tangential velocity was lowest. This finding is similar to that obtained by Viviani and Terzuolo (1982) for 2-D drawing arm movements and supports the notion that central constraints give rise to the relation between geometric and kinematic parameters of the trajectory.

Cognitive spatial-motor processes. 7. The making of movements at an angle from a stimulus direction: studies of motor cortical activity at the single cell and population levels.

Two rhesus monkeys were trained to move a handle on a two-dimensional (2-D) working surface either towards a visual stimulus ("direct" task) or in a direction orthogonal and counterclockwise (CCW) from the stimulus ("transformation" task), depending on whether the stimulus appeared dim or bright, respectively. Thus the direction of the stimulus (S, in polar coordinates) and the direction of the movement (M) were the same in the direct task but differed in the transformation task, such that M = S + 90 degrees CCW. The task (i.e. brightness) condition (k = 2, i.e. direct or transformation) and the direction of the stimulus (m = 8, i.e. 8 equally spaced directions on a circle) resulted in 16 combinations (k x m = 16 "classes") that were varied from trial to trial in a randomized block design. In 8 of these combinations the direction of the stimulus was the same for both tasks, whereas the direction of the movement was the same in the remaining 8 cases. The electrical signs of cell activity (N = 394 cells) in the arm area of the motor cortex (contralateral to the performing arm) were recorded extracellularly. The neural activity was analyzed at the single cell and neuronal population levels, and a modeling of the time course of single activity during the transformation task was carried out. We found the following. (a) Individual cells were active in both tasks; no cells were found that were active exclusively in only one of the two tasks. The patterns of single cell activity in the transformation task frequently differed from those observed in the direct task when the stimulus or the movement were the same. More specifically, cells could not be consistently classified as "movement"-or "stimulus"-related for frequently the activity of a particular cell would seem "movement-related" for a particular stimulus-movement combination, "stimulus-related" for another combination, or unrelated to either movement or stimulus for still another combination. Thus no real insight could be gained from such an analysis of single cell activity. (e) In a different analysis, we explored the idea that a changing directional signal could be detected in the time course of single cell activity during the reaction time. For that purpose we modeled the time course of single activity observed in the transformation task as a linear, weighted combination of influences from the direct task, taking the time patterns of cell activity during the stimulus, intermediate and movement directions in the direct task as estimates of the postulated directional influences.(ABSTRACT TRUNCATED AT 400 WORDS)

Cognitive spatial-motor processes. 4. Specification of the direction of visually guided isometric forces in two-dimensional space: information transmitted and effects of visual force-feedback.

The information transmitted (Ti) by the direction of two-dimensional (2-D) isometric forces at different stereoscopic depths was studied in 50 naive human subjects using an isometric manipulandum and random dot stereograms generated in a color display (Massey et al. 1988). Subjects viewed the display through appropriate color filters and perceived the image of a disk rotated about a horizontal axis on the frontal plane; the top of the disk was rotated around that axis by 15, 45, 60 and 80 degrees away from the subject. Each of these disks involved a different amount of stereoscopic depth perception which was lowest for the 15 degrees and highest for the 80 degrees tilt. Subjects were instructed to exert force in the direction of a visual target presented on the disk in a reaction time task. The instantaneous force exerted by the subjects on the manipulandum was shown on the disk in the form of a feedback cursor. Information transmitted, reaction time (RT) and systematic directional deviations were calculated. We found the following. (a) Ti increased with input information but at a lower rate; at the highest level of input information studied (5.91 bits), Ti was 4.1 bits at the 15 degrees tilt. This high value of Ti suggests that directional information for isometric force is processed very efficiently. However, this Ti was consistently lower than that transmitted by the direction of movement (Georgopoulos and Massay, 1988). (b) Ti did not differ significantly among the 15-60 degrees tilt but was 0.19 bits less for the 80 degrees tilt. RT did not differ among the 15-80 degrees tilts.(ABSTRACT TRUNCATED AT 250 WORDS)

Cognitive spatial-motor processes. 6. Visuomotor memory scanning.

Fourteen human subjects performed in a modified Sternberg memory-scanning task. First, they made a series of 2-6 movements in different directions from a central point towards peripheral lights on a planar working surface ("list trials"). Then, after a warning signal, one of the previous list stimuli, except the last, was presented again ("test trial"). Subjects were instructed to move in the direction of the stimulus which was presented next in sequence in the list. The mean reaction time (RT) in the test trials increased as a linear function of the number of movements, S, in the list: Mean RT (ms) = 105 + 205.8S (2 less than or equal to S less than or equal to 6). This finding suggests that the task involves memory scanning of visuomotor list items.

Mental rotation of the neuronal population vector.

A rhesus monkey was trained to move its arm in a direction that was perpendicular to and counterclockwise from the direction of a target light that changed in position from trial to trial. Solution of this problem was hypothesized to involve the creation and mental rotation of an imagined movement vector from the direction of the light to the direction of the movement. This hypothesis was tested directly by recording the activity of cells in the motor cortex during performance of the task and computing the neuronal population vector in successive time intervals during the reaction time. The population vector rotated gradually counterclockwise from the direction of the light to the direction of the movement at an average rate of 732 degrees per second. These results provide direct, neural evidence for the mental rotation hypothesis and indicate that the neuronal population vector is a useful tool for "reading out" and identifying cognitive operations of neuronal ensembles.