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A Touching Experience: Somatosensation
Image removed due to copyright considerations.Please see "Squire, Larry R., ed. Fundamental Neuroscience. 2nd ed. Boston,MA: Academic Press, 2003, Figure 25-14. ISBN: 0126603030."
Overview
I. Peripheral encoding in 2 pathways
II. Central Nervous System encoding in 2 pathways
III. Cortex: Basic organizational principles
IV. Cortex: Plasticity & its perceptual implications
Head lesioned the nerve in his own hand to feel how sensation returned as thenerve recovered. Found there were 2distinct recovery phases:
Image removed due to copyright reasons.
Protopathic --> Temperature and Pain
Epicritic --> Non-painful touch, spatially and temporally
precise sensations
Henry Head: The Vincent Van Gogh of Somatosensory Neuroscience
Distinct Pathways :Peripheral Encoding of
Fine Temporal & Spatial Info* Defining features of receptive field properties: Firing propert
ies & receptive field size
* Slowly adapting vs rapidly
adapting: Distinction?
* Why is this distinction needed?
Image removed due to copyright reasons.Please see "Squire, Larry R., ed. Fundamental Neuroscience.2nd ed. Boston, MA: Academic Press, 2003, Figure 25-3. ISBN: 012660303
0."
Peripheral Receptors:Slowly Adapting (SA), Merkel’s
* Merkel cells/disks, SA Type I-> Dense innervation of skin (100/cm2)-> Respond with SA discharge, sensitive to edges,
points and surface features-> Spatial rf size: 2-3 mm2* Perceptual abilitieswe need these for?‘2-Point Discrimination’
Images removed due to copyright reasons. Please see "Squire, Larry R., ed. Fundamental Neuroscience.2nd ed. Boston, MA: Academic Press, 2003, Figures 25-1 and 25-5. ISBN: 0126603030."
Peripheral Receptors:Slowly Adapting, Ruffini
* SA Type II (Ruffini corpuscles?)-> Only in humans-> 2-4 x less sensitive than SAI-> Respond to skin stretch
* Perceptual abilitieswe need these for?.
Image removed due to copyright reasons.Please see "Squire, Larry R., ed. Fundamental Neuroscience.2nd ed. Boston, MA: Academic Press, 2003, Figure 25-5. ISBN: 0126603030."
Peripheral Receptors: Rapidly Adapting/Meissner’s
Meissner’sCorpuscle
Image removed due to copyright reasons.
Peripheral Receptors: Pacinian Corpuscles
Pacinian Corpuscle
Image removed due to copyright reasons.
Peripheral Receptors: Anatomical/Structual Determinants
of Functional Capability
Image removed due to copyright reasons.
Structural Determinants of Displacement Sensitivity & Spatial/
Temporal Specificity
Images removed due to copyright reasons.Please see "Squire, Larry R., ed. Fundamental Neuroscience.2nd ed. Boston, MA: Academic Press, 2003, Figure 25-5. ISBN: 0126603030."
Structural Determinants ofDisplacement Sensitivity &
Spatial/Temporal Specificity
Image removed due to copyright reasons.Please see "Squire, Larry R., ed. Fundamental Neuroscience.2nd ed. Boston, MA: Academic Press, 2003. ISBN: 0126603030."
Distinct Pathways :Peripheral Encoding of
Pain &Temperature
Paradoxical Cold Hot stimuli applied to a very discrete point
on the skin can be perceived as cold in some cases…Why?
Distinct Pathways : Perception is not only a
‘Labeled Line’
• What is a labeled line?
• The Coca-Cola Illusion…
OverviewI. Peripheral encoding in 2 pathways
II. Central Nervous System encoding in 2 pathways
III. Cortex: Basic organizational principles
IV. Cortex: Plasticity & its perceptual implications
Image removed due to copyright reasons.
PNS vs CNS: Dorsal Root
* PseudounipolarNeuron
Image removed due to copyright reasons.
* Dorsal RootGanlgion* PNS/CNSdivision point
Dermatomes
* Dorsal roots cover a distinct body region* 4 distinct ascending segments of the cord
Image removed due to copyright reasons. Image removed due to copyright reasons.Please see "Squire, Larry R., ed.Fundamental Neuroscience.2nd ed. Boston, MA: Academic Press,2003, Figure 25-9. ISBN: 0126603030.
Entoumbences: Why?
Image removed due to copyright reasons.
Image removed due to copyright reasons.Please see "Squire, Larry R., ed.Fundamental Neuroscience.2nd ed. Boston, MA: Academic Press,2003, Figure 25-9. ISBN: 0126603030."
Spinal Cord:Segregation of Gray & White Matter
Image removed due to copyright reasons.
Segregation of Pathways forTouch & Pain
* Dorsal Column-Medial Lemniscus Pathway (DCML)& Anterolateral Pathway (AL)
Image removed due to copyright reasons. Please see "Squire, Larry R., ed. Fundamental Neuroscience. 2nd ed. Boston, MA:Academic Press, 2003, Figure 25-11. ISBN: 0126603030."
Spinal Cord:Segregation of Pathways for
Touch & Pain * Dorsal Column-Medial Lemniscus Pathway (DCML)
Image removed due to copyright reasons.Please see "Squire, Larry R., ed.Fundamental Neuroscience. 2nd ed. Boston, MA: Academic Press, 2003, Figure 25-11.ISBN: 0126603030."
Image removed due to copyright reasons.
Location of DCN & Medial Lemniscus
* DC projections synapse in thedorsal column nuclei
Images removed due to copyright reasons.
Spinal Cord:Segregation of Pathways for
Touch & Pain
Image removed due to copyright reasons.Please see "Squire, Larry R., ed. Fundamental Neuroscience.2nd ed. Boston, MA: Academic Press, 2003,Figure 25-11. ISBN: 0126603030."
Thalamus: Store Room of Relay& Modulatory Nuclei
Image removed due to copyright reasons.
Somatosensory Pathways:Thalamic Relay Nuclei
* Ventrobasal complex is a collection of somatosensory thalamic nuclei with distinct properties
* Tactile inputs from body (DCML)synapse on the ventral posterior
lateral nucleus (VPL), facial tactile inputs synapse in VPM
Image removed due to copyright reasons.
Somatosensory Pathways:Thalamic Relay Nuclei
* Ventrobasal complex is a collection of somatosensory thalamic nuclei with distinct properties
* Deep/proprioceptive inputsinput to regions surrounding the VPL, the ‘shell’ region, as opposed to the tactile’core’ region
Image removed due to copyright reasons. Please see "Squire, Larry R., ed. Fundamental Neuroscience. 2nd ed. Boston, MA: Academic Press, 2003, Figure 25-14. ISBN: 0126603030."
OverviewI. Peripheral encoding in 2 pathways
II. Central Nervous System encoding in 2 pathways
III. Cortex: Basic organizational principlesAreas, Maps, Columns and Magnification
IV. Cortex: Plasticity & its perceptual implications
Image removed due to copyright reasons.
Somatosensory Pathways:Cortical Areas
* Areas 3b and 1 receive VP Nucleus Core input, and
3a and 2 VP Shell input* Convergent intracortical con
nections predict area 2 rf properties
Image removed due to copyright reasons.Please see "Squire, Larry R., ed.Fundamental Neuroscience. 2nd ed. Boston, MA: Academic Press, 2003, Figure 25-14. ISBN: 0126603030."
Somatosensory Pathways: Cortical Areas
* 4 key distinct areas in thePost-central gyrus:Area 3b = SI -> discrete tactile rf Area 1
-> Similar to 3b, more RA rf Area 3a deep & proprioceptive
Area 2 touch + proprioception
Please see "Moore, C. I., C. Stern, S. Corkin, B. Fischl, A. Gray, B. Rosen, and A. M. Dale. "Segregation of somatosensory activation in the human hand area using fMRI."Journal of Neurophysiology 84 (2000): 558-569."
Somatosensory Cortex:Cortical Maps
* Initially motor maps were inferred by Hughlings Jackson (‘Jacksonian March’)
•Initially motor maps were inferred by Hughlings Jackson (‘Jacksonian March’)
* Head (1920), tactile mapsInferred from crude lesion patients
•Penfield, electrical stimulation and in surgery patient reports
* Penfield and S. Corkin, well- described lesions post-surgery
Image removed due to copyright reasons.Please see "Squire, Larry R., ed. FundamentalNeuroscience. 2nd ed. Boston, MA:AcademicPress, 2003, Figure 25-15. ISBN: 0126603030."
Visual Cortex: Cortical Columns
Discovered & explicated by Mountcastle: Cellsin a vertical dimension across the layers of the
neocortex tend to have the same rf properties
Images removed due to copyright reasons.
Somatosensory Cortex: Cortical Columns
* Orientation columns in V1
Image removed due to copyright reasons.Please see "Squire, Larry R., ed. Fundamental Neuroscience. 2nd
ed. Boston, MA: Academic Press, 2003. ISBN: 0126603030."
Cortical Isofrequency ColumnsAuditory Cortex
Image removed due to copyright reasons. Please see "Kilgard, M.P., and M. M. Merzenich. "Distrib
uted representation of spectral and temporal information in rat primary auditory cortex." Hearing Research 134 (1999), 16-28."
Somatosensory Cortex:Cortical Magnification
* Cortical Magnification Rule: Space devoted to a skin surface is inversely proportional to the size of the receptive field in that area (Sur et al., 1980)
Image removed due to copyright reasons.
Image removed due to copyright reasons.Please see "Squire, Larry R., ed.Fundamental Neuroscience.2nd ed. Boston, MA: Academic Press, 2003,Figure 25-15. ISBN: 0126603030."
Image removed due to copyright reasons.Please see "Sur, M, M. M. Merzenich, andJ. H. Kaas. "Magnification, receptive-field area, and "hypercolumn" size in areas 3b and1 of somatosensory cortex in owl monkeys."Journal of Neurophysiology 44 (1980): 295-311."
OverviewI. Peripheral encoding in 2 pathways
II. Central Nervous System encoding in 2 pathways
III. Cortex: Basic organizational principlesAreas, Maps, Columns and Magnification
IV. Cortex: Plasticity & its perceptual implications
Image removed due to copyright reasons.
Somatosensory Cortex:Adult Cortical Plasticity
Images removed due to copyright reasons.
Somatosensory Cortex:Adult Cortical Plasticity
Images removed due to copyright reasons.
Perceptual Consequences
* Phantom Limbs, reference zones
Image removed due to copyright reasons
Perceptual ConsequencesBeyond Phantom Limb?
* Increased spatial tactile resolution in ‘reference’ zones.First discoveredBy Teuber (founder of the Department)
* Possible cause?Image removed due to copyright reasons.
Effect of Massive Deafferentation: Spinal-Cord Injury
* Phantom body sensations
Effect of Massive Deafferentation:Cortical Plasticity
* Cortical activation maps to the phantom percept, but what’s the problem here? What’s the answer?
mage removed due to copyright reasons.Please see "Moore, C. I., C. E., Stern, C., Dunbar, S., Kostyk, A., Gehi, andS., Corkin. "Referred Phantom Sensations and Cortical ReorganizationAfter Spinal Cord Injury in Humans." PNAS USA 97 (2000): 14703-14708."
Effect of Massive Deafferentation: Cortical Plasticity
* Cortical activation maps to the phantom percept,Cortical Plasticity:Adaptive Effects
* Wang et al: Trained skin regions developbut what’s the problem here? What’s the answer?
Image removed due to copyright reasons. Please see "Moore, C. I., C. E., Stern, C.,Dunbar, S., Kostyk, A., Gehl, and S., Corkin."Referred Phantom Sensations and CorticalReorganization After Spinal Cord Injury inHumans." PNAS USA 97 (2000): 14703-14708."
Image removed due to copyright reasons.
Cortical Plasticity:Adaptive Effects
Wang et al: Trained skin regions developoverlapping rf.
* String instrument players have expanded representations of the‘picking’ hand
Image removed due to copyright reasons.Please see "Wang, X., M. M. Merzenich, K. Sameshima, and W. M. Jenkins. "Remodeling of hand representation in adult cortexdetermined by timing of tactile stimulation."Nature 378 (1995): 71-75."
OverviewI. Peripheral encoding in 2 pathways
II. Central Nervous System encoding in 2 pathways
III. Cortex: Basic organizational principlesAreas, Maps, Columns and Magnification
IV. Cortex: Plasticity & its perceptual implications
Image removed due to copyright reasons.