OBJECTIVES AND METHOD: The relation between body sway recorded through a stabilometric platform and the subjective report of steadiness was studied in 20 young and 20 elderly subjects and 20 neuropathic and 20 parkinsonian patients standing upright. The trials were performed under two stances (feet apart, feet together) and two visual conditions (eyes open, eyes closed). At the end of each trial, subjects scored their performance on a scale from 10 (complete steadiness) to 0 (fall). RESULTS: In all subjects, independently of the stance conditions, the larger the body sway the smaller the reported score. The function best fitting this relation was linear when sway was expressed on a logarithmic scale. The scoring reproducibility proved high both within and across subjects. Despite the different body sways and scores recorded under the different visual and postural conditions (eyes closed>eyes open, feet together>feet apart) in all groups of subjects and patients, the slopes of the relations between sway and score were broadly superimposable. In the normal subjects, the scores were slightly higher during eyes open than eyes closed trials for corresponding body sways. This was interpreted as a sign of perception of greater stability when vision was allowed. Parkinsonian patients swayed to a similar extent as normal subjects, and their scores were accordingly similar, both with eyes open and eyes closed. Neuropathic patients swayed to a larger extent than normal subjects, and their scores were matched appropriately. Although the slope of their relation with eyes closed was not different from that of normal subjects, with eyes open it was steeper and similar to that with eyes closed, suggesting that these patients did not feel more stable when they could take advantage of vision. CONCLUSIONS: The subjective evaluation of body sway, irrespective of stance condition, age, neuropathy, and basal ganglia disease, reflects the actual sway, and is inversely proportional to the logarithm of the sway value. The remarkable similarity of the relation between score and sway across the various groups of subjects with eyes closed indicates a common mode of sway evaluation, possibly based on integration of several sensory inputs. All groups except neuropathic patients seem to take advantage of the redundancy of the inputs. Basal ganglia integrity does not seem to have a role in the evaluation of sway. (+info)
Optical imaging of functional domains in the cortex of the awake and behaving monkey.
As demonstrated by anatomical and physiological studies, the cerebral cortex consists of groups of cortical modules, each comprising populations of neurons with similar functional properties. This functional modularity exists in both sensory and association neocortices. However, the role of such cortical modules in perceptual and cognitive behavior is unknown. To aid in the examination of this issue we have applied the high spatial resolution optical imaging methodology to the study of awake, behaving animals. In this paper, we report the optical imaging of orientation domains and blob structures, approximately 100-200 micrometer in size, in visual cortex of the awake and behaving monkey. By overcoming the spatial limitations of other existing imaging methods, optical imaging will permit the study of a wide variety of cortical functions at the columnar level, including motor and cognitive functions traditionally studied with positron-emission tomography or functional MRI techniques. (+info)
A theory of geometric constraints on neural activity for natural three-dimensional movement.
Although the orientation of an arm in space or the static view of an object may be represented by a population of neurons in complex ways, how these variables change with movement often follows simple linear rules, reflecting the underlying geometric constraints in the physical world. A theoretical analysis is presented for how such constraints affect the average firing rates of sensory and motor neurons during natural movements with low degrees of freedom, such as a limb movement and rigid object motion. When applied to nonrigid reaching arm movements, the linear theory accounts for cosine directional tuning with linear speed modulation, predicts a curl-free spatial distribution of preferred directions, and also explains why the instantaneous motion of the hand can be recovered from the neural population activity. For three-dimensional motion of a rigid object, the theory predicts that, to a first approximation, the response of a sensory neuron should have a preferred translational direction and a preferred rotation axis in space, both with cosine tuning functions modulated multiplicatively by speed and angular speed, respectively. Some known tuning properties of motion-sensitive neurons follow as special cases. Acceleration tuning and nonlinear speed modulation are considered in an extension of the linear theory. This general approach provides a principled method to derive mechanism-insensitive neuronal properties by exploiting the inherently low dimensionality of natural movements. (+info)
Ultrasonic vocalizations elicit orienting and associative reactions in preweanling mice.
On postnatal days (PND) 12 and 13, 90 male Swiss CD-1 mice were tested for orientation to 3 intensities of recorded ultrasounds while climbing an inclined wire grid surface. Motor responses and vocalization to replayed ultrasounds (55-75 kHz) of 20-, 40-, and 60-dB SPL indicated an intensity dependence. In Experiment 2, 138 pups were exposed to either contingent or noncontingent pairings of recorded ultrasounds of 55-75 kHz, averaging 40 dB, and mild inescapable footshocks, or taped vocalizations or footshocks only on PND 12, 14, or 16. At PND 18, subjects were tested for passive avoidance following exposure to the taped ultrasounds only upon entry into the dark side of a black-white compartment. Results suggested only overall, nonspecific effects of pretreatment to elicit responses antagonistic to motor activity. In Experiment 3, 36 pups at PND 15 were tested for passive avoidance with the ultrasound recordings of 40- or 80-dB onset upon entry to the dark compartment; a third group had no ultrasound exposure. A significant intensity effect confirmed that the ultrasounds had prepotent properties. (+info)
The physiological effects of monocular deprivation and their reversal in the monkey's visual cortex.
1. 1127 single units were recorded during oblique penetrations in area 17 of one normal, three monocularly deprived and four reverse sutured monkeys. 2. In all animals most cells outside layer IV c were orientation-selective, and preferred orientation usually shifted from cell to cell in a regular progressive sequence. 3. The presence in layer IV c of non-oriented, monocularly driven units, organized in alternating right-eye and left-eye 'stripes' (LeVay, Hubel & Wiesel, 1975) was confirmed. 4. Early monocular deprivation (2--5 1/2 weeks) caused a strong shift of ocular dominance towards the non-deprived eye. However, even outside layer IV c, neural background and some isolated cells could still be driven from the deprived eye in regularly spaced, narrow columnar regions. In layer IV c the non-deprived eye's stripes were almost three times wider, on average, than the deprived. 5. Later monocular deprivation (11--16 months) had no detectable influence on layer IV c but seemed to cause a small shift in ocular dominance outside IV c. Deprivation for 6 1/4 months in an adult had no such effect. 6. After early reverse suturing (at 5 1/2 weeks) the originally deprived eye gained dominance over cells outside layer IV c just as complete as that originally exercised by the eye that was first non-deprived. 7. The later reverse suturing was delayed, the less effective was recapture by the originally deprived eye. Reversal at 8 weeks led to roughly equal numbers of cells being dominated by each eye; fewer cells became dominated by the newly open eye after reverse suturing at 9 weeks and most of them were non-oriented; reversal at 38 1/2 weeks had no effect. 8. Binocular cells, though rare in reverse sutured animals, always had very similar preferred orientations in the two eyes. The columnar sequences of preferred orientation were not interrupted at the borders of ocular dominance columns. 9. Even within layer IV c there was evidence for re-expansion of physiologically determined ocular dominance stripes. After early reverse suture, stripes for the two eyes became roughly equal in width. Possible mechanisms for these changes are discussed. (+info)
Macaque SEF neurons encode object-centered directions of eye movements regardless of the visual attributes of instructional cues.
Macaque SEF neurons encode object-centered directions of eye movements regardless of the visual attributes of instructional cues. Neurons in the supplementary eye field (SEF) of the macaque monkey exhibit object-centered direction selectivity in the context of a task in which a spot flashed on the right or left end of a sample bar instructs a monkey to make an eye movement to the right or left end of a target bar. To determine whether SEF neurons are selective for the location of the cue, as defined relative to the sample bar, or, alternatively, for the location of the target, as defined relative to the target bar, we carried out recording while monkeys performed a new task. In this task, the color of a cue-spot instructed the monkey to which end of the target bar an eye movement should be made (blue for the left end and yellow for the right end). Object-centered direction selectivity persisted under this condition, indicating that neurons are selective for the location of the target relative to the target bar. However, object-centered signals developed at a longer latency (by approximately 200 ms) when the instruction was conveyed by color than when it was conveyed by the location of a spot on a sample bar. (+info)
Averaging and summation of influences on visually perceived eye level between two long lines differing in pitch or roll-tilt.
The presence of one or two long, dim, eccentrically-placed, parallel, pitched-from-vertical lines in darkness generates a systematic influence on the physical elevation that appears to correspond to eye level (VPEL). The influence of the line(s) in darkness is nearly as large as that produced by a complexly-structured, well-illuminated visual field (Matin L, Li W. Vis Res, 1994;34:311-330); oblique lines in a frontoparallel plane that strike the same projected orientations generate the same influences as those generated by pitched-from-vertical lines (Li W, Matin L. Perception, 1996;25:831-852). The two experiments described here examined the influence on the physical elevation of VPEL due to simultaneous viewing of two long lines of different pitch (Experiment 1) or two long lines of different obliquity in a frontoparallel plane (Experiment 2). Experiment 1 employed two long (66 degrees), simultaneously-presented, pitched-from-vertical lines in darkness on bilaterally symmetric locations at 25 degrees horizontal eccentricity, with each line at one of seven pitches in the range from -30 degrees to +30 degrees; VPELs were measured for all 49 possible pitch combinations. Experiment 2 was identically constructed, but employed oblique 2-line stimuli from a frontoparallel plane that struck the same projected orientations as did the pitched-from-vertical lines in Experiment 1. VPELs measured on four subjects in the two experiments were indistinguishable for corresponding conditions of pitch and obliquity. For a given pitch (obliquity) of one of the lines the elevation of VPEL increased linearly with the pitch (obliquity) of the second line. The VPEL for any 2-line combination is very close to the average of the VPELs for the two individual lines; a small amount of additive summation between the influences of the two lines was also found. Parallel and nonparallel 2-line stimuli appear to follow the same rules of combination. The results are clear in showing that the visual influence on VPEL is controlled by an opponent-process mechanism. (+info)
The role of orientation flights on homing performance in honeybees.
Honeybees have long served as a model organism for investigating insect navigation. Bees, like many other nesting animals, primarily use learned visual features of the environment to guide their movement between the nest and foraging sites. Although much is known about the spatial information encoded in memory by experienced bees, the development of large-scale spatial memory in naive bees is not clearly understood. Past studies suggest that learning occurs during orientation flights taken before the start of foraging. We investigated what honeybees learn during their initial experience in a new landscape by examining the homing of bees displaced after a single orientation flight lasting only 5-10 min. Homing ability was assessed using vanishing bearings and homing speed. At release sites with a view of the landmarks immediately surrounding the hive, 'first-flight' bees, tested after their very first orientation flight, had faster homing rates than 'reorienting foragers', which had previous experience in a different site prior to their orientation flight in the test landscape. First-flight bees also had faster homing rates from these sites than did 'resident' bees with full experience of the terrain. At distant sites, resident bees returned to the hive more rapidly than reorienting or first-flight bees; however, in some cases, the reorienting bees were as successful as the resident bees. Vanishing bearings indicated that all three types of bees were oriented homewards when in the vicinity of landmarks near the hive. When bees were released out of sight of these landmarks, hence forcing them to rely on a route memory, the 'first-flight' bees were confused, the 'reorienting' bees chose the homeward direction except at the most distant site and the 'resident' bees were consistently oriented homewards. (+info)