Perceptual Structure

L.A. Loren lloren at mitre.org
Mon Sep 18 09:58:35 EST 2000


While the study of phantom limbs and unilateral neglect are interesting,
they do not directly support the conclusion that we use an explicit
bodily representation. There are a growing number of researchers who
believe that we do not, in fact, make use of such internal
representations. Merleau-Ponty, in the "Structure of Behavior" and "The
Phenomenology of Perception" argues that we do not use such
representation and is based on several case studies. There was an
article in Science some years back (97 or 98?) by Rizolatti (sp?) et. al
in which it was argued that we store spatial information in a
body-centric visual/spatial (a combination of both) terms and not as a
kind of explicit 3D Cartesian coordinate system. There are also a number
of researchers that study  unilateral neglect who argue that we do not
have an explicit internal representation of the body (I do not have the
references handy, but can dig them up if you'd like).   

Once again, phantom limbs, unilateral neglect, and other pathological
cases are all interesting, but they do not directly support the claim
that we make use of an explicit internal representation of the body
during the course of our day to day activities (i.e. when we are "living
through" our bodies rather than thinking about them). While this has
been the most common view, it is still contested.

Cheers,
Lew

Ian Goddard wrote:
> 
> A little research at the National Library of Medicine PubMed
> website finds that the "body in the brain" idea I've proposed
> in the "Perceptual Structure" post seems to be a leading-edge
> theory in neuroscience (see first journal abstract below).
> 
> I recently acquired an important article in Scientific American
> (April 1992, pages 120-26) by Ronald Melzack on phantom limbs.
> He's proposed what the evidence clearly indicates, that the
> phantom-limb experience is explained by your perceived body
> being a model in your brain, a model we're born with, which
> explains why, for example, some people born with no limbs
> perceive limbs. The "body in the brain" model explains a
> wide range of otherwise anomalous phantom-limb experiences.
> Also, damage to brain regions associated with the perception
> of a given limb can cause a person to believe that limb is not
> part of them, but is an "alien limb." Logically, what we see as
> being "inside" or "outside" is a product of neurological mapping.
> Therefore, experiences where consciousness moves or expands into
> the area of the internal map defined as "outside myself" are
> perceived as an expansion of consciousness into external space,
> but it's explainable as the neurological program remapping the
> location defined as "inside myself" in its internal world map,
> rather than that consciousness expanding into external space.
> 
> Following the first abstract are other relevant medical-
> journal abstracts mostly on mapping the "body in the brain."
> 
> ===========================================================
> 
> Trends in Neuroscience, 1997 Dec;20(12):560-4
> 
> The body in the brain: neural bases of corporeal awareness.
> 
> Berlucchi G, Aglioti S
> 
> Dipartimento di Scienze Neurologiche, Universita di Verona, Italy.
> 
> Recent studies have begun to unravel the brain mechanisms
> that underlie the mental representation of the body.
> Imitation of movements by neonates suggests an implicit
> knowledge of the body structure that antedates the adult
> body schema. This can include inanimate objects that bear
> systematic relations to the body, as shown by the elimination
> from self awareness of a body part and its associated
> paraphernalia after selective brain lesions. Dynamic aspects
> of the body schema are revealed by spontaneous sensations
> from a lost body part as well as by orderly phantom sensations
> elicited by stimulation of body areas away from the amputation
> line and even by visual stimulation. The mechanisms of the
> body schema exhibit stability, since some brain regions seem
> permanently committed to representing the corresponding body
> parts in conscious awareness, and plasticity, since brain
> regions deprived of their natural inputs from a body part
> become reactive to inputs from other body parts.
> 
> ===========================================================
> 
> Proceedings of the National Academy of Sciences,
> U S A 2000 May 23;97(11):6167-72
> 
> Beyond re-membering: phantom sensations of congenitally
> absent limbs.
> 
> Brugger P, Kollias SS, Muri RM, Crelier G, Hepp-Reymond
> MC, Regard M
> 
> Department of Neurology and Institute of Neuroradiology,
> University Hospital Zurich, CH-8091 Zurich, Switzerland.
> pbrugger at npsy.unizh.ch
> 
> Phantom limbs are traditionally conceptualized as the
> phenomenal persistence of a body part after deafferentation.
> Previous clinical observations of subjects with phantoms of
> congenitally absent limbs are not compatible with this view,
> but, in the absence of experimental work, the neural basis
> of such "aplasic phantoms" has remained enigmatic. In this
> paper, we report a series of behavioral, imaging, and
> neurophysiological experiments with a university-educated
> woman born without forearms and legs, who experiences vivid
> phantom sensations of all four limbs. Visuokinesthetic
> integration of tachistoscopically presented drawings of
> hands and feet indicated an intact somatic representation
> of these body parts. Functional magnetic resonance imaging
> of phantom hand movements showed no activation of primary
> sensorimotor areas, but of premotor and parietal cortex
> bilaterally. Movements of the existing upper arms produced
> activation expanding into the hand territories deprived of
> afferences and efferences. Transcranial magnetic stimulation
> of the sensorimotor cortex consistently elicited phantom
> sensations in the contralateral fingers and hand. In
> addition, premotor and parietal stimulation evoked similar
> phantom sensations, albeit in the absence of motor evoked
> potentials in the stump. These data indicate that body
> parts that have never been physically developed can be
> represented in sensory and motor cortical areas. Both
> genetic and epigenetic factors, such as the habitual
> observation of other people moving their limbs, may
> contribute to the conscious experience of aplasic phantoms.
> 
> ===========================================================
> 
> Nature Neuroscience, 2000 Apr;3(4):358-65
> 
> A mapping label required for normal scale of body
> representation in the cortex.
> 
> Vanderhaeghen P, Lu Q, Prakash N, Frisen J, Walsh CA,
> Frostig RD, Flanagan JG
> 
> Department of Cell Biology and Program in Neuroscience,
> Harvard Medical School, Boston, Massachusetts 02115, USA.
> 
> The neocortical primary somatosensory area (S1) consists
> of a map of the body surface. The cortical area devoted to
> different regions, such as parts of the face or hands,
> reflects their functional importance. Here we investigated
> the role of genetically determined positional labels in
> neocortical mapping. Ephrin-A5 was expressed in a medial >
> lateral gradient across S1, whereas its receptor EphA4 was
> in a matching gradient across the thalamic ventrobasal (VB)
> complex, which provides S1 input. Ephrin-A5 had topographically
> specific effects on VB axon guidance in vitro. Ephrin-A5
> gene disruption caused graded, topographically specific
> distortion in the S1 body map, with medial regions contracted
> and lateral regions expanded, changing relative areas up to
> 50% in developing and adult mice. These results provide
> evidence for within-area thalamocortical mapping labels and
> show that a genetic difference can cause a lasting change in
> relative scale of different regions within a topographic map.
> 
> =============================================================
> 
> Neuroimage, 2000 Jan;11(1):36-48
> 
> Passive and active recognition of one's own face.
> 
> Sugiura M, Kawashima R, Nakamura K, Okada K, Kato T,
> Nakamura A, Hatano K, Itoh K, Kojima S, Fukuda H
> 
> Department of Nuclear Medicine and Radiology, IDAC,
> Tohoku University, Sendai, 980-8575, Japan.
> 
> Facial identity recognition has been studied mainly with
> explicit discrimination requirement and faces of social
> figures in previous human brain imaging studies. We
> performed a PET activation study with normal volunteers
> in facial identity recognition tasks using the subject's
> own face as visual stimulus. Three tasks were designed so
> that the activation of the visual representation of the
> face and the effect of sustained attention to the
> representation could be separately examined: a control-face
> recognition task (C), a passive own-face recognition task
> (no explicit discrimination was required) (P), and an
> active own-face recognition task (explicit discrimination
> was required) (A). Increased skin conductance responses
> during recognition of own face were seen in both task P
> and task A, suggesting the occurrence of psychophysiological
> changes during recognition of one's own face. The left
> fusiform gyrus, the right supramarginal gyrus, the left
> putamen, and the right hypothalamus were activated in
> tasks P and A compared with task C. The left fusiform
> gyrus and the right supramarginal gyrus are considered to
> be involved in the representation of one's own face. The
> activation in the right supramarginal gyrus may be
> associated with the representation of one's own face as
> a part of one's own body. The prefrontal cortices, the
> right anterior cingulate, the right presupplementary motor
> area, and the left insula were specifically activated
> during task A compared with tasks C and P, indicating that
> these regions may be involved in the sustained attention to
> the representation of one's own face. Copyright 2000 Academic
> Press.
> 
> =============================================================
> 
> Annu Rev Neurosci 2000;23:1-37
> 
> Cortical and subcortical contributions to activity-dependent
> plasticity in primate somatosensory cortex.
> 
> Jones EG
> 
> Center for Neuroscience, University of California, Davis 95616,
> USA. ejones at ucdavis.edu
> 
> [Medline record in process]
> 
> After manipulations of the periphery that reduce or enhance
> input to the somatosensory cortex, affected parts of the body
> representation will contract or expand, often over many
> millimeters. Various mechanisms, including divergence of
> preexisting connections, expression of latent synapses, and
> sprouting of new synapses, have been proposed to explain such
> phenomena, which probably underlie altered sensory experiences
> associated with limb amputation and peripheral nerve injury in
> humans. Putative cortical mechanisms have received the greatest
> emphasis but there is increasing evidence for substantial
> reorganization in subcortical structures, including the
> brainstem and thalamus, that may be of sufficient extent to
> account for or play a large part in representational plasticity
> in somatosensory cortex. Recent studies show that divergence of
> ascending connections is considerable and sufficient to ensure
> that small alterations in map topography at brainstem and
> thalamic levels will be amplified in the projection to the
> cortex. In the long term, slow, deafferentation-dependent
> transneuronal atrophy at brainstem, thalamic, and even cortical
> levels are operational in promoting reorganizational changes,
> and the extent to which surviving connections can maintain a
> map is a key to understanding differences between central and
> peripheral deafferentation.
> 
> ==============================================================
> 
> J Comp Neurol 2000 Jun 26;422(2):246-66
> 
> Rat somatosensory cerebropontocerebellar pathways: spatial
> relationships of the somatotopic map of the primary
> somatosensory cortex are preserved in a three-dimensional
> clustered pontine map.
> 
> Leergaard TB, Lyngstad KA, Thompson JH, Taeymans S, Vos BP,
> De Schutter E, Bower JM, Bjaalie JG
> 
> Department of Anatomy, Institute of Basic Medical Sciences,
> University of Oslo, N-0317 Oslo, Norway.
> 
> In the primary somatosensory cortex (SI), the body surface
> is mapped in a relatively continuous fashion, with adjacent
> body regions represented in adjacent cortical domains. In
> contrast, somatosensory maps found in regions of the
> cerebellar hemispheres, which are influenced by the SI
> through a monosynaptic link in the pontine nuclei, are
> discontinuous ("fractured") in organization. To elucidate
> this map transformation, the authors studied the organization
> of the first link in the SI-cerebellar pathway, the SI-pontine
> projection. After injecting anterograde axonal tracers into
> electrophysiologically defined parts of the SI, three-
> dimensional reconstruction and computer-graphic visualization
> techniques were used to analyze the spatial distribution of
> labeled fibers. Several target regions in the pontine nuclei
> were identified for each major body representation. The
> labeled axons formed sharply delineated clusters that were
> distributed in an inside-out, shell-like fashion. Upper lip
> and other perioral representations were located in a central
> core, whereas extremity and trunk representations were found
> more externally. The multiple clusters suggest that the
> pontine nuclei contain several representations of the SI map.
> Within each representation, the spatial relationships of the
> SI map are largely preserved. This corticopontine projection
> pattern is compatible with recently proposed principles for
> the establishment of subcortical topographic patterns during
> development. The largely preserved spatial relationships in
> the pontine somatotopic map also suggest that the transformation
> from an organized topography in SI to a fractured map in the
> cerebellum takes place primarily in the mossy fiber
> pontocerebellar projection. Copyright 2000 Wiley-Liss, Inc.
> 
> 
> ------------------------------------------------------------
> GODDARD'S JOURNAL: http://www.erols.com/igoddard/journal.htm
> ____________________________________________________________
> Asking the "wrong questions," challenging the Official Story
> 
> 
>






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