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PubMed1998

Fully automated establishment of stereotaxic image orientation in six degrees of freedom for technetium-99m-ECD brain SPECT.

UNLABELLED: Anatomical localization requires establishing an anatomical space within the image matrix. We developed a fast, fully automated method to establish the image orientation for 99mTc-ethylcysteinate dimer (ECD) brain SPECT images. METHODS: The image orientation of ECD brain SPECT images was established in four stages. First, the brain surface was edge-detected as an isosurface at an adaptive threshold. Second, a "convex hull" was determined for the isosurface to minimize regional variability in brain shape. A principal axis transformation and a symmetry vector analysis were applied to the convex hull to resolve the craniocaudal direction and to estimate the midsagittal plane. Third, the brain orientation was refined from this estimate by location of the interhemispheric fissure, the tentorial groove and the frontotemporal groove on the isosurface. Last, the intercommissural (anterior commissure-posterior commissure, or AC-PC) line was detected on the midsagittal slice, and the Talairach grid was scaled to fit the maximal brain dimensions from the AC-PC line. RESULTS: The average absolute errors were 2.3 degrees +/- 1.5 degrees and 1.08 mm +/- 1.11 mm for the midsagittal plane (n = 24) and 2.04 degrees +/- 0.80 degrees, 2.0% +/- 1.8% of the brain length and 2.3% +/- 2.2% of the brain height for the AC-PC line (n = 8). In addition, this program successfully established the image orientation in 94 of 100 clinical ECD brain SPECT studies. Processing time was <40 sec for 128 x 128 x 50 matrices on a DEC Alpha workstation. CONCLUSION: We have developed a fast, robust and fully automated method that determines the orientation of ECD brain SPECT images. This objective method of standardizing the image orientation should be useful for anatomical localization and clinical interpretation of these images.

Adult↗
PubMed1997

[Factors affecting active-life orientation among the elderly in a community in Japan and its relationship to social activities].

We surveyed a stratified random sample of 205 person from 45,500 residents, aged 65 years or older, in a city of Japan using an interview schedule including scales of active-life orientation, social activities and other covariates. A total of 157 (77%) participated in the study. The main results were as follows: 1) Significantly higher scores of active-life orientation were observed in those who currently worked, than in those who did not work in males and females (p < 0.05). In males, scores of active-life orientation were significantly higher in those who had hobbies than in those who did not (p < 0.05); in those who traveled during the past year than in those who did not (p < 0.05). 2) In multiple linear regression analysis, PGC scale scores positively and significantly correlated with score of active orientation in males and females (p < 0.05). Age negatively correlated with the scores in males. Scores of affiliation orientation positively correlated with scores of active orientation, and satisfaction with available social support negatively correlated with the scores in females (p < 0.05).

Aged↗
PubMed1998

Translation-invariant orientation tuning in visual "complex" cells could derive from intradendritic computations.

first distinguished "simple" from "complex" cells in visual cortex and proposed a processing hierarchy in which rows of LGN cells are pooled to drive oriented simple cell subunits, which are pooled in turn to drive complex cells. Although parsimonious and highly influential, the pure hierarchical model has since been challenged by results indicating that many complex cells receive excitatory monosynaptic input from LGN cells or do not depend on simple cell input. Alternative accounts of complex cell orientation tuning remain scant, however, and the function of monosynaptic LGN contacts onto complex cell dendrites remains unknown. We have used a biophysically detailed compartmental model to investigate whether nonlinear integration of LGN synaptic inputs within the dendrites of individual pyramidal cells could contribute to complex-cell receptive field structure. We show that an isolated cortical neuron with "active" dendrites, driven only by excitatory inputs from overlapping ON- and OFF-center LGN subfields, can produce clear phase-invariant orientation tuning-a hallmark response characteristic of a complex cell. The tuning is shown to depend critically both on the spatial arrangement of LGN synaptic contacts across the complex cell dendritic tree, established by a Hebbian developmental principle, and on the physiological efficacy of excitatory voltage-dependent dendritic ion channels. We conclude that unoriented LGN inputs to a complex cell could contribute in a significant way to its orientation tuning, acting in concert with oriented inputs to the same cell provided by simple cells or other complex cells. As such, our model provides a novel, experimentally testable hypothesis regarding the basis of orientation tuning in the complex cell population, and more generally underscores the potential importance of nonlinear intradendritic subunit processing in cortical neurophysiology.

Action Potentials↗
PubMed1998

The hemodynamic effects of mechanical prosthetic valve type and orientation on fluid mechanical energy loss and pressure drop in in vitro models of ventricular hypertrophy.

BACKGROUND AND AIMS OF THE STUDY: When choosing a prosthetic replacement for a natural heart valve, one objective should be to minimize the workload placed on the heart. This workload can be raised by fluid mechanical energy losses imposed by the valve. For a patient with left ventricular hypertrophy, certain aortic valve types and orientations could be hemodynamically superior to others. METHODS: This study used a control volume analysis to investigate the effects of prosthetic mechanical aortic valve type and orientation on fluid mechanical energy losses in four in vitro models of the left ventricular outflow/aortic inflow tract in various degrees of hypertrophy. Flow visualization studies were performed to qualitatively validate this analysis. The two most commonly used mechanical valve designs were studied: the St. Jude Medical (SJM) bileaflet valve and the Medtronic Hall (MH) tilting disk valve. Experiments were performed in pulsatile flow at a constant heart rate of 60 beats per min for five valve type/orientation combinations. The stroke volume was varied between 40 and 120 ml in five increments for each model and valve/orientation studied. RESULTS: Valve type and orientation was found to have a significant effect on energy losses in these models (p < 0.05). Valve/orientation combinations with leaflets or disks approximately parallel to the proximal flow direction created lower energy losses than others. The MH valve in the 180 degrees orientation caused significantly less energy losses and pressure drops (orifice and recovered) than any of the SJM valve/orientations studied (p < 0.05). The SJM and MH valves in the 0 degree orientation were responsible for significantly more energy loss than other valve/orientations studied (p < 0.05). An aortic inflow tract model with severe (45 degrees) curvature created significantly more energy loss (p < 0.05) than those with less curvature (15 and 30 degrees). However, the insertion of an obstruction simulating a hypertrophic tissue outgrowth caused much more energy loss than increasing the severity of outflow tract curvature from 15 to 45 degrees. Both orifice pressure drop and recovered pressure drop had excellent linear correlations with energy losses found in these models. CONCLUSIONS: These results imply that: (i) prosthetic valve type and orientation should be considered when replacing the aortic valve of a hypertropic patient; (ii) removal of obstructions within the aortic inflow tract will decrease ventricular workload; and (iii) the Doppler-estimated pressure gradients commonly use by cardiologists to assess the performance of a prosthetic valve, correlate very well with left ventricular energy loss and work load.

Aortic Valve↗
PubMed1999

Development of orientation preference in the mammalian visual cortex.

Recent experiments have studied the development of orientation selectivity in normal animals, visually deprived animals, and animals where patterns of neuronal activity have been altered. Results of these experiments indicate that orientation tuning appears very early in development, and that normal patterns of activity are necessary for its normal development. Visual experience is not needed for early development of orientation, but is crucial for maintaining orientation selectivity. Neuronal activity and vision thus seem to play similar roles in the development of orientation selectivity as they do in the development of eye-specific segregation in the visual system.

Animals↗
PubMed1994

Collator units: second-stage orientational filters.

Which parts of an image belong to the other parts? This has become known as the 'binding problem' and is almost as resistant to explanation now as it was over half a century ago, when the purely descriptive Gestalt rule of 'good continuation' and the like were formulated. The specific case of interest here is that of spatially sampled fragments of a continuous but partly occluded line. First-stage orientated visual filters with relatively small receptive fields (such as simple cells) make precise but essentially local measurements of the orientational properties of line fragments within their spatial domain. I suggest that these units act as 'tributary units', their outputs becoming the inputs to 'collator units', which are second-stage oriented filters whose function is to put together the local descriptions of the spatially distributed line fragments. The functional receptive field of the collator units would be the spatial sum of the receptive fields of the tributary units. If the tributary units all have the same orientation preference and their fields are axially aligned end to end, the receptive field of the corresponding collator unit would have the same orientation preference and width as its tributary units, but would be considerably longer. Psychophysical data are presented which are consistent with this model.

Animals↗
PubMed1981

The effect of stimulus orientation on the visual evoked potential in multiple sclerosis.

Visual evoked potential (VEP) latency was measured in 89 patients with multiple sclerosis (MS) using both a checkerboard stimulus and an alternating vertical grating. Thirty-seven patients had abnormal VEP latencies to the check stimulus, but 63 were classified as abnormal when the grating stimulus was employed. In an additional 22 MS patients, each eye was tested with a checkerboard stimulus, a vertical grating, and a horizontal grating to determine if edge orientation of the stimuli was responsible for the difference between grating and check diagnostic yields. The resulting diagnostic differences could be explained by taking into account the sinusoidal components of these stimuli. After equating gratings and checks for the fundamental Fourier component, each eye of 15 of the MS patients was retested with gratings in three orientations: vertical, horizontal, and oblique. Nine of the 15 patients had an orientation-dependent abnormality of VEP latency. The results suggest that MS causes an orientational imbalance in the human visual system and that VEP testing with stimuli in more than one orientation can increase the diagnostic yield in MS patients.

Adolescent↗
PubMed1987

Topographic organization of the orientation column system in large flat-mounts of the cat visual cortex: a 2-deoxyglucose study.

We developed a flat-mount technique in order to visualize, without additional reconstruction, the system of orientation columns in the cat visual cortex by using 2-deoxyglucose-autoradiography. Experimental animals were injected with 2-deoxyglucose and then stimulated for 45-60 minutes either with vertical or horizontal or oblique gratings alone or with vertical and horizontal gratings presented in alternation. In both areas 17 and 18 stimulation with either vertical or horizontal or oblique stripes produced similar and highly ordered patterns of parallel bands of increased 2-deoxyglucose uptake that were perpendicular to the boundaries of the areas. In area 17 they occasionally extended without interruption from the 17/18 border on the top of the lateral gyrus to the monocular segment in the splenial sulcus. Superposition of serial sections revealed that these bands were present in all cortical layers and in precise register along lines orthogonal to the lamination. The center-to-center spacing of the bands was 1.0-1.1 mm in area 17 and 1.2-1.4 mm in area 18. Stimulation with alternating vertical and horizontal contours led to a pattern the general organization of which resembled that induced by a single orientation but the spacing of which was reduced by a factor of 0.5. This strongly supports the concept that orientation is mapped in a system of parallel bands and argues against a recently formulated hypothesis that iso-orientation bands extend like spokes from centers that lack orientation selectivity (Braitenberg and Braitenberg, Biol. Cybern. 33:179-186, '79). Another characteristic feature, revealed by the flat-mount technique, was a periodic variation of 2-deoxyglucose uptake along the bands that gave them a beaded appearance. The mean center-to-center distance between adjacent beads on the same band was in the range of 0.9-1.2 mm and remained unchanged when horizontal and vertical gratings were presented in alternation. We propose that these beads reflect another columnar system whose features have yet to be determined.

Animals↗
PubMed1978

Specificity of litter odors in the control of home orientation among kittens.

The specificity of maternal-home cage odors governing home orientation was tested in 8- to 11-day-old kittens. Kittens were first tested for home orientation from the adjacent corner in their own home cages and cages of other mothers with litters of the same age. The majority of kittens oriented successfully in their own cages but not in strange mothers' cages. They then lived for 48 hr in the strange mothers' cages. At the end of this time they showed no improvement in orientation in their own home cages. Moreover, after an additional 24 hr in their own home cages they showed no improvement in their own home cages. Home orientation involves 2 odor components: 1 general to different mothers and 1 specific to each mother.

Animals↗
PubMed1994

Quantification of directional and orientational selectivities of visual neurons to moving stimuli.

Directional and orientational components usually coexist and are mixed in the cell's overall responses when moving optical stimuli are used to study the response characteristics of visual neurons. While these two properties were quantified with all the previous methods for data analysis, their effects could not be efficiently separated from each other, and thus the analyses were imperfect. In this paper, theoretical evidence and examples are provided to show the defects of the old methods. In order to separate the two components completely, we propose to apply optimal regression analysis with the sine-cosine function series as the fundamental variables. Based on this separation, we defined the orientational selectivity as variation of response strength with orientation and performed integration and averaging to quantify the two properties [cf. Eqs. (5) and (6)]. The present method has the advantages of completeness and accuracy, and can detect some details which would have been missed by other methods. An explanation of the intrinsic implications of the method and our comprehension of directional and orientational selectivities and preferred direction and orientation are also given.

Algorithms↗
PubMed1994

Activity of neurons in Forel's field H during orienting head movements in alert head-free cats.

Single unit activities were recorded in Forel's field H (FFH) at the mesodiencephalic junction during orienting head movements in two alert cats under head-free conditions. Recordings were made of 63 neurons of which 20 showed phasic firing that preceded the onset of head movements by 20-100 ms and was temporally related to the dynamic phase of the orienting head movement. Nineteen of these neurons showed a preference for upward movements, while the remaining neuron preferred downward movements. Activities during orienting movements in eight different directions (each separated by 45 degrees) were systematically analyzed for 12 of the 19 upward-preferring neurons. The activities were broadly tuned; in most of the neurons, maximum activity was observed for direct upward movements (+90 degrees), but significant activity was also observed for ipsilateral and contralateral oblique upward movements (+45 degrees and +135 degrees). In these cases, the increase in activity preceded the onset of the movement. Some increase in activity was also observed for ipsilateral and contralateral horizontal, oblique downward and downward movements. However, the increase in activity in the latter cases occurred simultaneously with or lagged behind the onset of the movement and was often preceded by a decrease in activity. The same pattern of directional tuning was observed in the EMG of the biventer cervicis muscle, a target of FFH neurons. The preferred directions of the 12 upward-preferring neurons were estimated by calculating the vector sum of the activity and were distributed between +68 degrees and +108 degrees. The same amount of activity was observed for ipsilateral and contralateral oblique upward movements, suggesting that FFH neurons on both sides of the brainstem are equally activated even during oblique orienting. Input from the ipsilateral superior colliculus was investigated in 18 neurons, all of which were orthodromically activated with a latency of 0.8-1.8 ms, suggestive of a mono- or disynaptic excitatory connection. Seven neurons were identified as descending projection neurons by antidromic activation from the ipsilateral medullary reticular formation. Repetitive microstimulation of unilateral FFH induced oblique upward head movements and an accompanying torsional component, while simultaneous bilateral stimulation at comparable stimulus strength induced purely upward head movements. These results strongly suggest that the vertical component of orienting head movements is encoded by equal bilateral activation of the FFH.

Animals↗
PubMed1992

Aberrant retinal projections to midbrain targets mediate spared visual orienting function in hamsters with neonatal lesions of superior colliculus.

Rodents, cats, and most nonmammalian vertebrates with bilateral tectal deafferentation or ablation in adulthood are extremely deficient at orienting to visual stimuli; yet animals with neonatal lesions of superficial layers of the superior colliculus (SC) show partial sparing of this response, particularly for targets in the central visual field. In this study, we sought to determine whether these spared orienting abilities are mediated by aberrant retinal projections to the remaining intermediate layers of the SC, or whether visual cortex (VC) mechanisms or alternative behavioral strategies are responsible. Neonatal golden hamsters received either bilateral heat lesions of the SC (rlSC), or a heat lesion of the right SC and enucleation of the right eye (rSCrE). This latter procedure causes axons from the left eye to recross the tectal midline and terminate in the "wrong" (left) SC (Schneider 1973). As adults, both groups of hamsters were extremely deficient in visually guided approach to stationary targets, although rlSC-lesioned hamsters showed some sparing for central field targets and rSCrE-lesioned hamsters often made wrong-direction turns for targets in the left peripheral field. We then subjected both groups of neonatally lesioned hamsters to bilateral aspiration lesions of the VC. Retesting showed no change in visual orienting behavior as a result of the cortical lesions. Labeling of the optic tract with horseradish peroxidase (HRP) revealed abundant aberrant retinal projections to remaining intermediate layers of the SC and thalamic nucleus lateralis posterior (LP), as well as supernormal innervation of pretectal nuclei, the dorsal terminal nucleus of the accessory optic tract, and the ventral nucleus of the lateral geniculate body (LGv). We conclude that the spared visual orienting capabilities of hamsters with rlSC and rSCrE lesions are mediated by the aberrant midbrain projections, and that cortical mechanisms are not involved in spared visual orienting functions following these neonatal lesions.

Animals↗
PubMed1984

Geniculate orientation biases seen with moving sine wave gratings: implications for a model of simple cell afferent connectivity.

Orientation bias of cat dorsal lateral geniculate (LGN) neurones varied with the spatial frequency of a moving sine wave grating. At low spatial frequencies there was little orientation bias, whereas near the high-frequency limit, the dependence on orientation was marked. It is proposed that, if such cells were to drive the cortical inhibitory interneurones responsible for the orientation sensitivity of striate simple cells, it would explain many distinguishing features of cortical cells besides their orientation sensitivity.

Animals↗
PubMed1994

Effects of spaceflight on ocular counterrolling and the spatial orientation of the vestibular system.

We recorded the horizontal (yaw), vertical (pitch), and torsional (roll) eye movements of two rhesus monkeys with scleral search coils before and after the COSMOS Biosatellite 2229 Flight. The aim was to determine effects of adaptation to microgravity on the vestibulo-ocular reflex (VOR). The animals flew for 11 days. The first postflight tests were 22 h and 55 h after landing, and testing extended for 11 days after reentry. There were four significant effects of spaceflight on functions related to spatial orientation: (1) Compensatory ocular counterrolling (OCR) was reduced by about 70% for static and dynamic head tilts with regard to gravity. The reduction in OCR persisted in the two animals throughout postflight testing. (2) The gain of the torsional component of the angular VOR (roll VOR) was decreased by 15% and 50% in the two animals over the same period. (3) An up-down asymmetry of nystagmus, present in the two monkeys before flight was reduced after exposure to microgravity. (4) The spatial orientation of velocity storage was shifted in the one monkey that could be tested soon after flight. Before flight, the yaw axis eigenvector of optokinetic afternystagmus was close to gravity when the animal was upright or tilted. After flight, the yaw orientation vector was shifted toward the body yaw axis. By 7 days after recovery, it had reverted to a gravitational orientation. We postulate that spaceflight causes changes in the vestibular system which reflect adaptation of spatial orientation from a gravitational to a body frame of reference. These changes are likely to play a role in the postural, locomotor, and gaze instability demonstrated on reentry after spaceflight.

Animals↗
PubMed1977

Biases for oriented moving bars in lateral geniculate nucleus neurons of normal and stripe-reared cats.

Visual receptive fields of 42 LGN cells from normal cats and 110 cells from striped cylinder-reared kittens were studied with the aid of a computer controlled optical system. In the normal cats, ten of the 42 cells were weakly biased for orientation of the visual stimulus when tested with bars swept through the receptive field. Of those ten, eight were classified as transient. The orientation preferences of the ten biased units appeared randomly distributed around the clock. Of the LGN cells from the cylinder-reared group, about half of the transient cells had weak biases for orientation; only 7% of the sustained cells had biases. The orientation preferences of the biased LGN cells in the stripe-reared animals were either parallel to or orthogonal to the stripes each animal saw during its time in the conditioning cylinder. In 16 out of 18 of the biased LGN cells it was found that increasing the velocity of the test target reduced or eliminated the bias apparent at the lower velocity. For some LGN cells special techniques, such as inhibition of activated discharge, were needed to reveal orientation biases. The results described here, considered with data from others, suggest a role for the corticofugal projection in modulating the responses of some LGN cells.

Action Potentials↗
PubMed1981

Effect of neonatal unilateral enucleation on the development of orientation selectivity in the primary visual cortex of normally and dark-reared kittens.

The developmental properties of 573 neurones have been investigated in the primary visual cortex of eight binocularly intact and twelve unilaterally enucleated kittens. It is shown that removal of one eye at birth alters the development of orientation selectivity observed in the presence or absence of visual experience. In 6-week-old deprived kittens, there remain significantly more orientation selective cells in enucleated than in binocularly deprived kittens. These deprivation-resistant cells respond preferentially to horizontal or vertical orientations and are recorded mainly in the cortex contralateral to the remaining eye. In six-week-old kittens with visual experience, the process of tuning maturation appears to be unaffected by unilateral enucleation at birth. However, a larger over-representation of horizontal and vertical orientation preferences is observed in uniocular kittens than in binocularly intact kittens, suggesting that the development of oblique orientation preference depends upon the presence of binocular afferents in the visual pathway.

Animals↗
PubMed1981

Effect of body tilt on receptive field orientation of simple visual cortical neurons in unanesthetized cats.

The receptive field (RF) orientation of 53 simple visual cortical neurons was determined by recording the activity of single cells during presentation of stationary bars of light. An RF tuning curve was constructed for each cell by averaging the neural discharge resulting from the repeated presentation of a number of slit orientations. RF curves were then determined again, following a 45 degrees roll tilt of the entire head and body, and subsequently after the return of the animal to the original horizontal position. RF tuning curves were typical of what others have found to characterize simple cells, and were highly replicable on the return to the starting position. In 73% of the cells studied, the RF orientation after tilt remained unaltered relative to the head axis (+/- 15 degrees); in the remaining 27% of the cells RF orientations either under- or over-shot the retinal tilt by more than 15 degrees, and in some cases by as much as 45 degrees. These results support the hypothesis that the well documented vestibular inputs to visual cortex play a role in modifying the RF orientation selectively of visual cortical neurons, and suggest that such information may be an important neurophysiological substrate underlying visual spatial constancy mechanisms.

Animals↗
PubMed1985

Orientation bias of brisk-transient y-cells of the cat retina for drifting and alternating gratings.

Brisk-transient ganglion cells of the cat's retina were examined for orientation bias using two different stimuli: drifting gratings and alternating gratings, both of fixed contrast (50%) and fixed temporal frequency (2 Hz). Some cells were strongly biassed for both stimuli, some were not biassed for either while still others were strongly biassed for only one or other stimulus. The preferred orientations for the two types of grating tended to be the same, on average, but substantial differences were not uncommon. A systematic preference for radially-oriented gratings was evident when the stimulus was drifting but there was an additional preference for tangentially-oriented gratings when the stimulus was alternating. Orientation bias for drifting gratings often extended over a broad range of spatial frequencies and was maximum near the resolution limit. For alternating gratings, bias was evident only at the highest spatial frequencies. Results indicate that the arrangement of receptive field components responsible for linear and nonlinear kinds of behaviour may sometimes possess different axes of symmetry.

Animals↗