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T A Zeffiro

Publications and source records attributed to T A Zeffiro.

At least 19 recordsLinked to original sources
PubMed1999

Utilizing hemodynamic delay and dispersion to detect fMRI signal change without auditory interference: the behavior interleaved gradients technique.

A major problem associated with the use of functional magnetic resonance imaging (fMRI) is the attendant gradient noise, which causes undesirable auditory system stimulation. A method is presented here that delays data acquisition to a period immediately after task completion, utilizing the physiological delay and dispersion between neuronal activity and its resulting hemodynamic lag. Subjects performed finger movements with the gradients off, followed by a rest period with the gradients on. This resulted in task-related signals comparable to those obtained with concurrent task performance and image data acquisition. This behavior interleaved gradients technique may be particularly useful for the studies involving auditory stimulation or overt verbal responses.

Acoustic Stimulation↗
PubMed1998

Neural systems underlying learning and representation of global motion.

We demonstrate performance-related changes in cortical and cerebellar activity. The largest learning-dependent changes were observed in the anterior lateral cerebellum, where the extent and intensity of activation correlated inversely with psychophysical performance. After learning had occurred (a few minutes), the cerebellar activation almost disappeared; however, it was restored when the subjects were presented with a novel, untrained direction of motion for which psychophysical performance also reverted to chance level. Similar reductions in the extent and intensity of brain activations in relation to learning occurred in the superior colliculus, anterior cingulate, and parts of the extrastriate cortex. The motion direction-sensitive middle temporal visual complex was a notable exception, where there was an expansion of the cortical territory activated by the trained stimulus. Together, these results indicate that the learning and representation of visual motion discrimination are mediated by different, but probably interacting, neuronal subsystems.

Adult↗
PubMed1998

Regional cerebral blood flow during auditory responsive naming: evidence for cross-modality neural activation.

One issue of continuing debate in language research concerns whether the brain holds separate representations for semantic information through the auditory vs visual modalities. Regardless of whether we hear, see or read meaningful information, our brains automatically activate both auditory and visual semantic associations to the sensory input. The prominent models for how the brain makes these cross-modality associations holds that semantic information conveyed through either sensory input modality is represented in a shared semantic system comprising the traditionally identified language areas in the brain. A few recent case reports as well as activation imaging studies, have challenged this notion by demonstrating category-specific organization within the semantic system in spatially discrete brain regions. Neither view posits a role for primary sensory cortices in semantic processing. We obtained positron emission tomographic (PET) images while subjects performed an auditory responsive naming task, an auditory analog to visual object naming. Subjects heard and responded to descriptions of concrete objects while blindfolded to prevent visual stimulation. Our results showed that, in addition to traditional language centers, auditory language input produced reciprocal activation in primary and secondary visual brain regions, just as if the language stimuli had entered in the visual modality. These findings provide evidence for a distributed semantic system in which sensory-specific semantic modules are mutually interactive, operating directly onto early sensory processing centers.

Acoustic Stimulation↗
PubMed1998

Neural activation during acute capsaicin-evoked pain and allodynia assessed with PET.

The PET H2 15O-bolus method was used to image regional brain activity in normal human subjects during intense pain induced by intradermal injection of capsaicin and during post-capsaicin mechanical allodynia (the perception of pain from a normally non-painful stimulus). Images of regional cerebral blood flow were acquired during six conditions: (i) rest; (ii) light brushing of the forearm; (iii) forearm intradermal injection of capsaicin, (iv) and (v) the waning phases of capsaicin pain; and (vi) allodynia. Allodynia was produced by light brushing adjacent to the capsaicin injection site after ongoing pain from the capsaicin injection had completely subsided. Capsaicin treatment produced activation in many discrete brain regions which we classified as subserving four main functions: sensation-perception (primary somatosensory cortex, thalamus and insula); attention (anterior cingulate cortex); descending pain control (periaqueductal grey); and an extensive network related to sensory-motor integration (supplementary motor cortex, bilateral putamen and insula, anterior lobe and vermis of the cerebellum and superior colliculus). Comparison of the noxious and non-noxious stimuli yielded several new insights into neural organization of pain and tactile sensations. Capsaicin pain, which had no concomitant tactile component, produced little or no activation in secondary somatosensory cortex (SII), whereas light brushing produced a prominent activation of SII, suggesting a differential sensitivity of SII to tactile versus painful stimuli. The cerebellar vermis was strongly activated by capsaicin, whereas light brush and experimental allodynia produced little or no activation, suggesting a selective association with C-fibre stimulation and nociceptive second-order spinal neurons. The experimental allodynia activated a network that partially overlapped those activated by both pain and light brush alone. Unlike capsaicin-induced pain, allodynia was characterized by bilateral activation of inferior prefrontal cortex, suggesting that prefrontal responses to pain are context dependent.

Acute Disease↗
PubMed1997

The role of posterior parietal cortex in visually guided reaching movements in humans.

Positron emission tomography (PET) was used to identify the brain areas involved in visually guided reaching by measuring regional cerebral blood flow (rCBF) in six normal volunteers while they were fixating centrally and reaching with the left or right arm to targets presented in either the right or the left visual field. The PET images were registered with magnetic resonance images from each subject so that increases in rCBF could be localized with anatomical precision in individual subjects. Increased neural activity was examined in relation to the hand used to reach, irrespective of field of reach (hand effect), and the effects of target field of reach, irrespective of hand used (field effect). A separate analysis on intersubject, averaged PET data was also performed. A comparison of the results of the two analyses showed close correspondence in the areas of activation that were identified. We did not find a strict segregation of regions associated exclusively with either hand or field. Overall, significant rCBF increases in the hand and field conditions occurred bilaterally in the supplementary motor area, premotor cortex, cuneus, lingual gyrus, superior temporal cortex, insular cortex, thalamus, and putamen. Primary motor cortex, postcentral gyrus, and the superior parietal lobule (intraparietal sulcus) showed predominantly a contralateral hand effect, whereas the inferior parietal lobule showed this effect for the left hand only. Greater contralateral responses for the right hand were observed in the secondary motor areas. Only the anterior and posterior cingulate cortices exhibited strong ipsilateral hand effects. Field of reach was more commonly associated with bilateral patterns of activation in the areas with contralateral or ipsilateral hand effects. These results suggest that the visual and motor components of reaching may have a different functional organization and that many brain regions represent both limb of reach and field of reach. However, since posterior parietal cortex is connected with all of these regions, we suggest that it plays a crucial role in the integration of limb and field coordinates.

Adult↗
PubMed1997

A direct comparison of PET activation and electrocortical stimulation mapping for language localization.

Mapping eloquent language cortex in presurgical patients typically is accomplished using highly invasive direct cortical stimulation techniques. Functional imaging during language activation using positron emission tomography (PET) is a promising, noninvasive alternative that requires validation. In seven patients undergoing surgical evaluation for intractable epilepsy, we performed both direct cortical stimulation and PET activation mapping of language cortex using identical tasks. MRI, PET, and CT scans were coregistered to directly compare the location of language centers determined by cortical stimulation versus activation PET. We found that cortical regions that showed increased cerebral blood flow during both visual and auditory naming tasks were located in the same regions as subdural electrodes which disrupted language during electrical stimulation. Cortical regions underlying electrodes that did not disrupt language also showed no consistent changes in regional cerebral blood flow during PET activation. Used cautiously, PET activation produces language maps similar to those obtained with direct cortical stimulation, with more complete brain coverage and considerably less invasion.

Adolescent↗
PubMed1996

Abnormal processing of visual motion in dyslexia revealed by functional brain imaging.

It is widely accepted that dyslexics have deficits in reading and phonological awareness, but there is increasing evidence that they also exhibit visual processing abnormalities that may be confined to particular portions of the visual system. In primate visual pathways, inputs from parvocellular or magnocellular layers of the lateral geniculate nucleus remain partly segregated in projections to extrastriate cortical areas specialized for processing colour and form versus motion. In studies of dyslexia, psychophysical and anatomical evidence indicate an anomaly in the magnocellular visual subsystem. To investigate the pathophysiology of dyslexia, we used functional magnetic resonance imaging (fMRI) to study visual motion processing in normal and dyslexic men. In all dyslexics, presentation of moving stimuli failed to produce the same task-related functional activation in area V5/MT (part of the magnocellular visual subsystem) observed in controls. In contrast, presentation of stationary patterns resulted in equivalent activations in V1/V2 and extrastriate cortex in both groups. Although previous studies have emphasized language deficits, our data reveal differences in the regional functional organization of the cortical visual system in dyslexia.

Adult↗
PubMed1996

Functional mapping of human learning: a positron emission tomography activation study of eyeblink conditioning.

Regional cerebral blood flow (rCBF) was measured using positron emission tomography during eyeblink conditioning in young adults. Subjects were scanned in three experimental conditions: delay conditioning, in which binaural tones preceded air puffs to the right eye by 400 msec; pseudoconditioning, in which presentations of tone and air puff stimuli were not correlated in time; and fixation rest, which served as a baseline control. Compared with fixation, pseudoconditioning produced rCBF increases in frontal and temporal cortex, basal ganglia, left hippocampal formation, and pons. Learning-specific activations were observed in conditioning as compared with pseudoconditioning in bilateral frontal cortex, left thalamus, right medial hippocampal formation, left lingual gyrus, pons, and bilateral cerebellum; decreases in rCBF were observed for bilateral temporal cortex, and in the right hemisphere in putamen, cerebellum, and the lateral aspect of hippocampal formation. Blood flow increased as the level of learning increased in the left hemisphere in caudate, hippocampal formation, fusiform gyrus, and cerebellum, and in right temporal cortex and pons. In contrast, activation in left frontal cortex decreased as learning increased. These functional imaging results implicate many of the same structures identified by previous lesion and recording studies of eyeblink conditioning in animals and humans and suggest that the same brain regions in animals and humans mediate multiple forms of associative learning that give meaning to a previously neutral stimulus.

Adult↗
PubMed1996

Locating the motor cortex on the MRI with transcranial magnetic stimulation and PET.

Transcranial magnetic stimulation with a focal coil was used to map the cortical representation of a hand muscle in four healthy subjects. In each subject, the three-dimensional locations of the magnetic stimulation positions and about 400 positions on the surface of the head were digitized. The amplitude-weighted center of gravity of each subject's map was found, and a line perpendicular to the local head surface was projected inward. The digitized heads were registered with the subjects' MRIs using the scalp contours. The coordinate transformations yielded by this process were used to map the stimulation positions and the perpendicular line into the MRIs. Brain areas imaged with positron emission tomography (PET) and 15O-labeled water, activated by movement of the same muscle, were registered with the MRIs using the brain contours. In all cases, the magnetic stimulation lines encountered the surface of the brain at the anterior lip of the central sulcus and ran along the precentral gyrus a few millimeters anterior to the central sulcus, coming within 5-22 mm of all the PET activation maxima. This technique demonstrates the accuracy of transcranial magnetic stimulation for locating the primary motor area.

Adult↗
PubMed1996

The visual deficit theory of developmental dyslexia.

Dyslexia is an impairment in reading that can result from an abnormal developmental process in the case of developmental dyslexia or cerebral insult in the case of acquired dyslexia. It has long been known that the clinical manifestations of developmental dyslexia are varied. In addition to their reading difficulties, individuals with developmental dyslexia exhibit impairments in their ability to process the phonological features of written or spoken language. Recently, it has been demonstrated with a variety of experimental approaches that these individuals are also impaired on a number of visual tasks involving visuomotor, visuospatial, and visual motion processing. The results of these studies, as well as the anatomical and physiological anomalies seen in the brains of individuals with dyslexia, suggest that the pathophysiology of developmental dyslexia is more complex than originally thought, extending beyond the classically defined language areas of the brain. Functional neuroimaging is a useful tool to more precisely delineate the pathophysiology of this reading disorder.

Awareness↗
PubMed1996

Functional mapping of human memory using PET: comparisons of conceptual and perceptual tasks.

An experiment is reported in which regional cerebral blood flow (rCBF) as measured using positron emission tomography (PET) as participants performed conceptual and perceptual memory tasks. Blood flow during two conceptual tests of semantic cued recall and semantic association was compared to a control condition in which participants made semantic associations to nonstudied words. Analogously, rCBF during two perceptual tasks of word fragment cued recall and word fragment completion was compared to a word fragment nonstudied control condition. A direct comparison of conceptual and perceptual tasks showed that conceptual tasks activated medial and lateral left hemisphere in frontal and temporal regions as well as the lateral aspect of bilateral inferior parietal lobule. Perceptual tasks, in contrast, produced relatively greater activation in right frontal and temporal cortex as well as bilateral activation in more posterior regions. Comparisons of the memory tasks with their control conditions revealed memory-specific deactivations in left medial and superior temporal cortex as well as left frontal cortex for both conceptual tasks. In contrast, memory-specific deactivations for both perceptual fragment completion tests were localized in posterior regions including occipital cortex. Results from this and other functional imaging experiments provide evidence that conceptual and perceptual memory processes are subserved, at least in part, by different neurological structures in the human brain.

Adult↗
PubMed1995

Regional cerebral blood flow changes in motor cortical areas after transient anesthesia of the forearm.

To study the effect of deafferentation on cortical areas activated by movement of the proximal muscles, we measured regional cerebral blood flow with positron emission tomography and 15O-labeled water. Flexion-extension movements of the right elbow before deafferentation were associated with an increase of regional cerebral blood flow in the primary sensorimotor area bilaterally, posterior supplementary motor area bilaterally, ipsilateral cerebellum, contralateral putamen, premotor area, anterior cingulate area, and posterior parietal region. Transient anesthesia of the right forearm induced by ischemic block caused an increase of regional cerebral blood flow in the primary sensorimotor area bilaterally at rest, but there was no change of regional cerebral blood flow with movement, indicating that the movement-related change in cerebral blood flow was reduced. These findings are consistent with increased excitability of neurons as a result of deafferentation. In the supplementary motor area, anesthesia did not induce any change in regional cerebral blood flow at rest, but there was a decline with movement, again indicating a reduction of the change in cerebral blood flow related to movement. This might be due to a reduction in sensory feedback because of the anesthesia.

Adult↗
PubMed1995

Parametric analysis of functional neuroimages: application to a variable-rate motor task.

Positron emission tomography (PET) has proven to be a powerful tool in identifying the functional neuroanatomy underlying cognitive and sensorimotor processing. In this paper, we present a method for mathematically modeling the changes in regional cerebral blood flow (rCBF) as a function of experimental parameters using step and linear functions. PET was used to measure rCBF in six subjects who tracked a target moving with constant amplitude across a computer screen at four different frequencies. Each subject tracked the target by flexing and extending the wrist. Two scans were performed at each frequency. The data for each subject were normalized by the mean blood flow in each scan and scaled to the mean blood flow at rest. Scaled rCBF was regressed onto movement frequency to identify voxels which had either a significant linear or step function response to the frequency of movement. A group analysis was also performed to identify significant functional changes common to all subjects. Significant rCBF increases in relation to movement frequency were found in the supplementary motor area, primary motor cortex, premotor cortex, thalamus, and cerebellum and localized using the Talairach atlas. Habituation of responses was not observed.

Adult↗
PubMed1995

Functional MRI during word generation, using conventional equipment: a potential tool for language localization in the clinical environment.

OBJECTIVE: To test the accuracy of bilateral language mapping using a standard clinical magnetic resonance (MR) imaging device during word generation. DESIGN: A study of normal volunteers. SETTING: Volunteers from the Washington, DC, area. PARTICIPANTS: Nine normal, right-handed, native English speakers (four women, five men, mean age 31 years). INTERVENTIONS: During four MR acquisition periods, subjects would alternately rest and silently generate words. Sagittal MR images covered the middle and inferior frontal gyri, insulae, and part of the temporal and parietal lobes bilaterally. MAIN OUTCOME MEASURES: (1) Anatomic maps of task-related signal changes obtained by comparing, in each voxel, the signal during word generation and rest periods, and (2) analysis of the time course of the signal. RESULTS: Maximum responses were in the left hemisphere, mainly in the frontal lobe (Broca's area, premotor cortex, and dorsolateral prefrontal cortex) but also in posterior regions such as Wernicke's area. In agreement with previous studies, some degree of task-related changes was present in a subset of the corresponding regions in the right hemisphere. CONCLUSION: Despite certain limitations, it is possible, using widely available MR equipment, to obtain results consistent with previous studies. The technique may have important implications for assessment of cognitive functions in patients with neurologic disorders in a clinical environment.

Adult↗
PubMed1994

Head surface digitization and registration: a method for mapping positions on the head onto magnetic resonance images.

We have developed a method for mapping positions on the head, such as anatomical landmarks, electrode locations, and stimulation sites, onto magnetic resonance (MR) images of the head. This method is based on the registration of two representations of the head surface: a series of contours obtained from MR images and a set of points measured from the head. The three-dimensional coordinates of each head point were acquired with the use of a magnetic digitizer, whose source was removed from the equipment and mounted on top of the subject's head. This arrangement seemed less uncomfortable for the subject than head immobilization and allowed the acquisition of many points without compromising the precision of the measurements. The digitized head surface was registered to MR image head contours using a surface registration algorithm. The registration provided the rotation and translation parameters needed for mapping head positions onto MR images. The precision of this mapping method has been estimated to be in the range of 3 to 8 mm. This method has been used to map dipole sources in electroencephalography and magneto-encephalography and to impose maps of scalp sites used in transcranial magnetic stimulation onto MR and PET images of the brain.

Adult↗
PubMed1994

Head movement in normal subjects during simulated PET brain imaging with and without head restraint.

UNLABELLED: Head movement during brain imaging is recognized as a source of image degradation in PET and most other forms of medical brain imaging. However, little quantitative information is available on the kind and amount of head movement that actually occurs during these studies. We sought to obtain this information by measuring head movement in normal volunteers. METHODS: Head position data were acquired for 40 min in each of 13 supine subjects with and without head restraint. These data were then used to drive a mathematically simulated head through exactly the same set of movements. The positions of point sources embedded in this head were computed at each location and these data summarized as movement at FWHM in each of the three coordinate directions. RESULTS: Head movement increased with the length of the sampling interval for studies of either type (with or without head restraint), but the amount and rate of increase with restraint was much smaller. In contrast, head movement during consecutive, short sampling intervals was small and did not increase with time. Spatial gradients in head movement were detected within each study type, and significant spatial differences in head movement were found between study types. CONCLUSIONS: Head movements in normal, supine subjects, though small, can cause the effective resolution of a brain imaging study to appear to vary in space and time. These effects can be reduced significantly with head restraint and may also be reduced by dividing the acquisition of a single image into a sequence of short images (instead of a single long image), aligning these images spatially and summing the result.

Adult↗