Greg Detre
Sunday, 06 January, 2002
Dr Iles, St Hughes, week 1
somatosens NN � harder because you can�t feed it input so easily
generally hard to reproduce stimuli
don�t forget hair follicles, e.g. in hair animals
somatosensory system mor eheterogenous than other systems
e.g. star-nosed mole � nasal protuberances filled with mechanoreceptors
helps detect vibrations of insect inside burrow
tactile forces
microneurography � microstimulation
sharpened tungsten electrode into nerve + record from single unit
very difficult if there are any movements � tedious
once recording, use it to stimulate
appears that the unit you stimulate affects just recording from
ask the subject what they report
RA2 = PC, SA2 = Ruffini
1 = small receptive field, 2 = big
19th century histology, stain with silver, hence naming
not easy to square up the 4 physiologies with histology
mesentery � connective tissue holding guts etc. � contains PC
difficult to distinguish SA1-Merkel and RA1-Meissner
crossing � medulla vs gracile-cuneate???
also descending pathway down the lemniscular sysm, though it may be more direct
in vis system, there are more connections back from cortex to LGN than into it from retina � in awake animal, acts to control the transmission at a higher level � like an attentive mechanism
somatosens � analogous with dorsal col nuclei perhaps
skin stretch � glue threads linking 2 fingers + pull � subjects report fingers flexing
Ruffini plays kinesthetic role
PC � other animals don�t use tools, but monkeys have them
also just signal that something has happened when you touch something � and on a wide scale because large receptive field � what might they do with them???
hair + Meissner � flutter
also vibrissae
biophysics of ion channels in hair follicles � new information
gene family of degenerins in mouse genome � if knocked out, they can still hear, but one of the receptor types in hairs stops working, so probably >1 hair receptor type
skin hierarchy 3b, 1, SII
Kaas � topograph representation more complicated � separate maps, clearest in 3b, less clear in 2 because muscle afferents etc.
reason for >1 map is that they represent different information
parallel processing
in vis sysm, the topographic representation is retained a small way down the parallel paths
Iles thinks there�s quite a lot of hierarchy built into the system
divergent streams of processing
auditory system is parallel from early on, primary and cortex
3 topographic maps, then 2 parallel � what + where
usually believed that the spinothalamic (anterolateral) (pain, temperature + touch) system is � more ancient than lemniscal
spinal injury impairs complex touch, not anaesthetic
PPC also involved in motor control
mechanoreceptors� role in object manipulation + surface analysis
different functional stream � see fMRI � separate areas for shape + roughness (Roland et al 1998)
different tasks �/span> different parts of PPC
length/shape/roughness with hand � motor task, hence PPC
passive non-motor task would have been interesting
potential for fMRI to continue to improve is good
need bigger magnets, bigger computers, head stabilisation
even 1mm or so is too rough for columnar organisation
from PPC � ventral pre-motor areas � primary motor cortex � spinal cord
kinesthesia � sensing limb position + movement � many are propriocepttive receptors (joints + muscles) but some are cutaneous � straddles touch + proprioception
proprioception defined in terms of receptor (responds to position/movements of body parts)
are layers 5+6 part of S1??? y (not Brodmann�s area)
all of neocortex has 6-layered architecture
difficult to differentiate cytoarchitecturally
outputs to striatum � striatum is involved in motor control
(we can tell through lesions: Parkinson�s, Huntingdon�s (degeneration of striatum)), but indirectly
basal ganglia (some down spine) but mainly to cortex (mainly pre-motor + planning)
vision what stream <=> surface analysis (e.g. wood/smooth)
don�t know how linked to somatosens
do know about motor � some visual illusions fool ventral perception stream but do not influence motor behaviour
some motor control probably is influenced by ventral visual stream and so is subject to illusions
e.g. grip force is related to vision: size, texture, full etc.
sensory 8 tutorials
1: somatosens (ignore pain)
2+ vis � parallel, stereopsis
2 auditory � localisation
1 motor � reaching (next) - research exam questions + decrees re focusing on object recognition
insects are very small, yet they can still localise sounds (microseconds temporal differentials)
integrate with vision??? layers 5+6??? kinesthesia a type of proprioception??? motor??? can you trace from skin back to cortex??? N
why are there waypoints (e.g. LGN???) ???
threshold hearing � �nm
(posterior parietal � dorsal visual stream)
how many human typoes of hair cells??? unimportant
serial/parallel??? why >1 maps???
sII � stimulus recognition
Brodman vs Brodmann???
PNAS online
striate = BG???