Perceptual Structure

Ian Goddard igoddard at erols.mom
Sun Sep 17 09:39:54 EST 2000


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


  
  






More information about the Neur-sci mailing list