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Biomedical subjects

F H Baker

Publications and source records attributed to F H Baker.

18 recordsLinked to original sources
PubMed2001

Direction of gaze while walking a simple route: persons with normal vision and persons with retinitis pigmentosa.

PURPOSE: The purpose of this study was to determine whether persons with advanced vision impairment, when walking an unfamiliar route, visually sample the environment in a different manner than do persons with normal vision. METHODS: Direction of gaze was measured in six persons with retinitis pigmentosa (RP) and in three persons with normal vision as they walked an unfamiliar, obstacle-free route while viewing the environment in a head-mounted display. RESULTS: Persons with RP fixated over a larger area in the environment and at different features than did persons with normal vision. Persons with normal vision directed their gaze primarily ahead or at the goal, whereas persons with RP directed their gaze at objects on the walls, downward, or at the layout (i.e., edge-lines or boundaries between walls). The results also showed a significant negative correlation between the horizontal visual field extent of the RP subjects and the proportion of downward-directed fixations. CONCLUSIONS: Persons with advanced vision impairment as a result of RP visually sample the environment in a manner different from persons with normal vision.

Adult↗
PubMed1999

Relationship between laminar topology and retinotopy in the rhesus lateral geniculate nucleus: results from a functional atlas.

The primary focus of this paper is the abrupt transition that occurs midway through the rhesus lateral geniculate nucleus (LGN) from six layers posteriorly (conventionally numbered 1-6, ventral to dorsal) to four layers anteriorly. At this transition, layers 4 and 6 fuse into a single layer, as do layers 3 and 5, requiring an inversion of the stacking order of the cell categories making up layers 4 and 5. To understand the topology of this transition and its relationship to geniculate retinotopy, we have created a functional atlas of a rhesus LGN that affords three-dimensional views of morphology and retinotopy at a resolution of 25 microm. The projection of the path of the transition into visual space is highly biased toward lower visual fields, intersecting the upper vertical meridian at 6.4 degrees , the horizonal meridian at 15.4 degrees, and the lower vertical meridian at 25.0 degrees. Between inclinations of -31 degrees and 55 degrees, layers 3 and 5 merge through an elongated tear in layer 4 that subsumes the optic disk gap and extends medially and laterally; elsewhere, layers 4 and 6 merge through a tear in layer 5. These tears cause substantial violations of retinotopy and laminar integrity, so the inversion of layers 4 and 5 requires that the forces establishing retinotopy and grouping by cell class be locally overcome during morphogenesis. The transition and associated tears are evaluated in the context of recent computational models of geniculate morphogenesis. We have also used the atlas to estimate the borders of the binocular (55 approximately 62 degrees) and monocular (91 approximately 97 degrees) visual fields. Files containing the atlas are made publicly available on a website.

Algorithms↗
PubMed1998

Reorganization of sensory modalities evoked by microstimulation in region of the thalamic principal sensory nucleus in patients with pain due to nervous system injury.

Stimulation of the somatosensory system is more likely to evoke pain in patients with chronic pain after nervous system injury than in patients without somatosensory abnormalities. We now describe results of stimulation through a microelectrode at microampere thresholds (threshold microstimulation; TMIS) in the region of the human thalamic principal sensory nucleus (ventral caudal; Vc) during operations for treatment of movement disorders or of chronic pain. Patients were trained preoperatively to use a standard questionnaire to describe the location (projected field) and quality of sensations evoked by TMIS intraoperatively. The region of Vc was divided on the basis of projected fields into areas representing the part of the body where the patients experienced chronic pain (pain affected) or did not experience chronic pain (pain unaffected) and into a control area located in the thalamus of patients with movement disorders and no experience of chronic pain. The region of the Vc was also divided into a core region and a posterior-inferior region. The core was defined as the region above a standard radiologic horizontal line (anterior commissure-posterior commissure line; ACPC line) where the majority of cells responded to innocuous somatosensory stimulation. The posterior-inferior area was a cellular area posterior and inferior to the core. In both the core and the posterior-inferior regions, the proportion of sites where TMIS evoked pain was larger in pain-affected and unaffected areas than in control areas. The number of sites where thermal (warm or cold) sensations were evoked was correspondingly smaller, so that the total of pain-plus-thermal (sensation of warmth or cold) sites was the same in all areas. Therefore, sites pain where stimulation evoked pain in patients with neuropathic pain (i.e., pain following an injury to the nervous system) may correspond to sites where thermal sensations were evoked by stimulation in patients without somatosensory abnormality.

Brain Mapping↗
PubMed1996

Laminar and retinotopic organization of the macaque lateral geniculate nucleus: magnocellular and parvocellular magnification functions.

The laminar morphology and electrophysiologically determined retinotopic organization of a single rhesus macaque lateral geniculate nucleus (LGN) were reconstructed on series of coronal, sagittal, and horizontal cuts through a three-dimensional computer representation of the nucleus. Neurons were counted in this same nucleus, allowing the magnification functions (cells/degree2 as functions of eccentricity) of magnocellular and parvocellular layers to be determined after eliminating the effects of nonuniform volume shrinkage. Parvocellular magnification was approximately 10,000 times higher in the foveola than in the far periphery. On average, magnocellular neurons made up 2.6% of the LGN in the central 2 degrees (but probably a smaller fraction in the central fovea). The magnocellular portion increased steadily with eccentricity to 27% in the far periphery. Thus the magno/parvo ratio increases from foveola to far periphery by a factor of at least 14. The parvocellular magnification function matches estimates of cortical magnification, whereas the density of magnocellular afferents to cortex increases monotonically with eccentricity. At the posterior pole of the nucleus, the numbers of layers are reduced through a fusion of two layers and the disappearance of one or two others, a feature that may be associated with the foveal ipsilateral hemifield representation.

Animals↗
PubMed1993

Neurons in the area of human thalamic nucleus ventralis caudalis respond to painful heat stimuli.

A population of neurons in the area of human thalamic nucleus ventralis caudalis (Vc) respond to noxious heat stimuli. In the cutaneous core of Vc 6% (6/108) of recorded neurons had a significantly greater response to noxious heat stimuli than to innocuous control stimuli. Half of these neurons (n = 3) also responded to innocuous cold stimuli. Within the region posterior and inferior to the cutaneous core of Vc 5% (4/77) of neurons responded exclusively to noxious heat stimuli. Cells responding to noxious heat were recorded at a greater proportion (66%) of sites where painful sensations were evoked by microstimulation than at sites where nonpainful sensations were evoked (1.5%). The results suggest that neurons in the region of human Vc mediate the sensory aspect of pain.

Electric Stimulation↗
PubMed1993

Thermal and pain sensations evoked by microstimulation in the area of human ventrocaudal nucleus.

1. We have studied the sensations evoked by threshold microstimulation (TMS) in the area of the human principal sensory nucleus of the thalamus [ventralis caudalis (Vc)] in patients (n = 11) undergoing stereotactic surgery for the treatment of movement disorders and pain. Preoperatively, patients were trained to describe somatic sensory stimuli using a standard list of descriptors. This same list was used to describe sensations evoked intraoperatively by thalamic microstimulation. Stimulation sites (n = 216) were defined by location within the area where the majority of cells had a reproducible response to innocuous cutaneous stimulation (core region) or in the cellular area posterior and inferior to the core region (posteroinferior region). 2. TMS-evoked sensations were categorized as paresthetic if the descriptors "tingle," "vibration," or "electric current" were chosen by the patient to describe the sensation and as thermal/pain if the descriptors "cool," "warm," "warm and cool," or "pain" were chosen. Thermal/pain sensations were evoked by stimulation in 82% (9/11) of patients and at 19% of sites studied. These results suggest that thalamic microstimulation can evoke thermal/pain sensations reproducibly across patients. 3. Thermal/pain sensations were evoked more frequently by stimulation at sites in the posteroinferior region (30%) than by stimulation at sites in the core region (5%). Nonpainful thermal sensations composed the majority of thermal/pain sensations evoked by stimulation in both the core (80%) and posteroinferior regions (86%). Sites where stimulation evoked pain and nonpainful cool sensations were found anterior to the area where nonpainful warm sensations were evoked. Thermal/pain sensations were evoked at sites located medially near the border between the core and posteroinferior regions. 4. Radiologic techniques were used to determine the presumed nuclear location of stimulation sites. Thermal/pain sensations were evoked less frequently by stimulation in the part of Vc included in the core region than by stimulation in any of the following: the part of Vc included in the posteroinferior region, ventralis caudalis portae nucleus, ventralis caudalis parvocellularis nucleus, or the white matter underlying the ventral nuclear group. 5. The location of the sensation evoked by stimulation [projected field (PF)] varied widely in size. PFs were categorized as large if they involved more than one part of the body (e.g., face and arm) or if they crossed at least one joint proximal to the metacarpophalangeal joint or to the metatarsophalangeal joint. PFs were more frequently large at sites where thermal/pain sensations were evoked by TMS (33%) than at those where paresthesia were evoked (6%).(ABSTRACT TRUNCATED AT 400 WORDS)

Brain Mapping↗
PubMed1990

Educational methodology in dealing with animal rights and welfare in public service.

Animal rights and animal welfare have biological, economic, social, philosophical, emotional, political, legal and policy dimensions. Hundred of organizations are active in some aspect of these issues. Viewpoints range in a continuum from animal rights advocates to livestock producers. One long-range goal is to increase understandings of both the benefits and the costs of animal rights and animal welfare for individuals and society. In the short-range, solutions and (or) alternatives for crisis situations are needed. Key aspects for using education as a means to solve these problems are 1) characterization of the issue(s), 2) identification of the audience(s), 3) selection of communications media and channels, and 4) development of appropriate educational materials. Task forces of educators and clientele for audience involvement are essential in planning and testing educational methods. When situations involve political, legal, and policy aspects, two task forces are needed: 1) a multidisciplinary educational group of scientists and educators to prepare objective usable information, and 2) an action group of clientele to communicate potential impacts of political, legal or policy action. Liaison between two groups is very important. Contemporary examples are presented.

Agriculture↗
PubMed1987

The primate globus pallidus: neuronal activity related to direction of movement.

Neurons in the arm areas of the external and internal segments of the globus pallidus (GPe and GPi) and the ventral pallidum (VP) have been examined in a visuomotor step-tracking task. This task, which was similar to that used previously to examine neurons in the arm area of the putamen, dissociated the direction of movement from the pattern of muscle activity associated with the movement. The major finding of the present study is that, as in the putamen, the activity of almost half of the neurons in GPe and GPi was related to the direction of movement. Cells with overall patterns of activity similar to muscle were rare, although many neurons had static and/or dynamic load effects which resembled those seen in muscle. Responses of neurons to load application have also been examined in this paradigm in order to determine the nature of possible somatosensory input. Short-latency "sensory" responses to load application were found in pallidum as previously in putamen, but, by contrast, they occurred somewhat later and included bidirectional responses. Similar proportions of cells in GP and putamen were related to static loads. Some VP neurons appeared to encode information about specific features of the trials, but the majority of responses were nonspecific suggesting relations to more general features of the task.

Animals↗
PubMed1987

The primate nucleus basalis of Meynert: neuronal activity related to a visuomotor tracking task.

The activity of neurons in the nucleus basalis of Meynert (nbM), both the compact (nbMc) and interstitial (nbMi) components, has been examined in monkeys trained to perform a visuomotor step-tracking task. This study was carried out in the same animals and with the same task used to examine neuronal activity in the external and internal segments of globus pallidus (GPe and GPi) and ventral pallidum (VP). The presumed interstitial cells that are located within the laminae surrounding GPe and GPi and identified physiologically by their similarity with nbMc neurons, are referred to as border cells. A major finding of this study is that a large proportion of nbMc and border cells were active in relation to either the step-tracking movements or to load application. Moreover, a high proportion of the responses of border neurons were differential for opposite directions of load and movement. The percentages of directionally specific border and nbMc neurons were considerably less than for GP, with border neurons having more directionally specific responses than nbMc neurons. The similarity between border and GP neuronal properties in this task suggests that both may receive similar sensorimotor afferent input. In the compact portion of nbM, nonspecific neuronal responses following each behavioral event in the paradigm were common. These responses appeared to have been modified by and may have been contingent upon association with reinforcement.

Animals↗
PubMed1975

Spatial and chromatic properties of neurons subserving foveal and parafoveal vision in rhesus monkey.

The response properties of neurons in the region of striate cortex subserving central retina (0 degrees-2 degrees) and in a region of representation of parafoveal retina (4 degrees-7 degrees) were studied in unanesthetized paralyzed macaque monkeys. Neurons sensitive to the orientation of the stimulus in the visual field (simple, complex, and hypercomplex), and neurons lacking orientation selectivity (concentric, and a new class termed uniform) were found. In foveal cortex non-oriented cells were more numerous, and orientation sensitive cells had less strict spatial stimulus requirements than in parafoveal cortex. Most neurons received a monocular input, either exclusively or very predominantly. Three types of neurons were recognized on the basis of their responses to chromatic stimuli. (1) Luminosity neurons (about half the population) gave the same qualitative response to all effective wayelengths and had a spectral sensitivity similar to that of the macaque, determined behaviorally. Cells with all spatial types of receptive fields, except simple, occurred in this group. (2) Spectrally-treated neurons also responded in the same manner to different wavelengths, but over a narrower range than luminosity neurons, and their maximal sensitivity was shifted toward one or the other end of the visible spectrum. All tuned neurons had uniform or complex receptive field. (3) Spectrally-opponent neurons were either excited or inhibited by long wavelengths and responded in the opposite manner to short wavelengths. For cells with uniform or complex receptive fields the two opponent systems were coextensive. Simple or concentric neurons often had dual-opponent organization. The distribution of functional types among different cortical layers was similar in parafoveal and foveal cortex. The functional attributes of ocular dominance and orientation sensitivity were found to be statistically independent dimensions of cortical organization. On the other hand, the correlation between spatial and chromatic properties did not vary between different cytoarchitectonic layers, a finding suggesting that these neuronal properties depend on conjoined projectional and intracortical connecting mechanisms.

Animals↗
PubMed1975

The representation of the visual field in the lateral geniculate nucleus of Macaca mulatta.

Microelectrode recording techniques were used to investigate the projection of the visual field into the lateral geniculate nucleus (LGN) of Macaca mulatta. The data were used to construct charts plotting visual direction, designated in terms of azimuth and elevation, onto sections of the nucleus cut in coronal, sagittal and horizontal Horsley-Clarke planes. The projection of the horizontal meridian divides the LGN along its plane of symmetry into a medial-superior half having negative elevations and a lateral-inferior half having positive elevations. Elevations become more positive or negative with distance from this plane. Azimuths closest to the vertical meridian are located posteriorly, while the most peripheral azimuths are found at the anterior pole. Two families of surfaces representing visual directions of constant azimuth and elevation are described. Visual field zones of increasing eccentricity are represented serially along the posterior-anterior axis of the LGN, with the foveal area restricted to the posterior pole and the monocular crescent projecting to the anterior pole. The mapping is completely continuous across the horizontal meridian. The edges of the stacked cell laminae exposed around the periphery of the LGN form an oval band which receives the projection of the perimeter of the contralateral hemifield. The vertical meridian is represented by the posterior two-thirds of this band, while the periphery of the hemifield projects to the anterior third. The central visual field out to the optic disc is represented by six cell layers, while the rest of the binocular field projects to four layers only (2 parvocellular and 2 magnocellular). The monocular crescent is represented by one parvocellular and one magnocellular layer. Features associated with the projection column of the optic disc are integrated into the transition from six to four layers. Details of the receptive field topography in the vicinity of the optic disc discontinuities indicate that these gaps are produced by intralaminar mechanisms. The magnification factor (mm-3/steradian) increased monotonically from peripheral visual fields to the foveal center, varying over a range of three decades. This range is intermediate between those derived from data reported in the literature for the retina and the striate cortex. The ratio of LGN magnifications at any two angular eccentricities is a power function, with an exponent of 1.34, of the corresponding ratio of retinal ganglion cell densities. Similarly, the ratio of cortical magnifications (mm-2/steradian) at any two eccentricites is a power function, with an exponent of 1.35, of the corresponding ratio of LGN magnifications.

Animals↗