Somatosensory System and Multisensory Integration - Cross Modal Cognition - Lecture Notes, Study notes for Brain and Cognitive Science. Maulana Azad National Institute of Technology
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dharmadaas1 January 2013

Somatosensory System and Multisensory Integration - Cross Modal Cognition - Lecture Notes, Study notes for Brain and Cognitive Science. Maulana Azad National Institute of Technology

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Somatosensory System and Multisensory Integration, Cutaneous Mechanoreceptors, Receptor to Thalamus, Spinal Cord to Thalamus, Somatosensory Thalamus, Thalamus to Somatosensory Cortex, Orientation Tuning, Receptive Fields...
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Somatosensory system and multisensory integration • General introduction of receptor and cortical structure • Functional properties of receptors and cortical neurons

• Tactile sensitivity: 2 point threshold task – Visual influences in body schema - Haggard

• Tactile object recognition – Active vs. passive touch – Exploratory procedures – Vision and touch in object recognition

• Comparing vision and touch – Models for integrating visual and tactile information

Cutaneous mechanoreceptors • Meissner’s corpuscle

– Pressure or slow pushing • Merckle cells

– flutter • Pacinian corpuscle

– rapid vibration • Ruffini endings

– stretching

From receptor to thalamus • Fibres carry signal from receptor in the finger to the thalamus via the spinal cord

• Lateralisation of the body is mainly maintained in the spinal cord

• Two pathways of fibres in the spinal cord • Medial lemniscal pathway for propriocpetion and touch • Spinothalamic pathway for temperature and pain

From spinal cord to thalamus • Mechano-receptor dendrites progress up the spinal cord

• They synapse in the gracile and cuneate nucleus in the brain stem

• Then cross over the midline of the spinal cord and ascend to nuclei in the thalamus

Somatosensory thalamus • Sensory thalamus is somatotopically organised

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[Mountcastle & Henneman, J. Comp. Neurol., 1952]

From thalamus to somatosensory cortex • Connections from thalamus fan out to areas of the somatosensory cortex (S1

and maybe S2)

•  Somatosensory cortex is mapped according to body parts

• Response tuning in cells of S1

Orientation tuning in S1 • Receptive fields of neuron in cortex are tuned to orientation of edge placed on

hand

Hyvarinin & Poranen (1978)

Receptive fields of cortical neurons • RF sizes depend on site on the body

• Larger receptive fields away from finger tips

• Smaller receptive fields mean greater sensory sensitivity

• More cortex devoted to areas with smaller RFs

Measuring sensitivity in touch

Tactile acuity measured by 2-point discrimination and thresholds along body

Cortical plasticity • Training on the 2-point task can reduce threshold

• Training caused increase in cortical representation of stimulated hand

Recanzone et al. (J. Neurophysiology, 1992)

Remapping somatosensory cortex Phantom limb

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• Patient with a limb amputation • the somatosensory areas originally associated with the limb were remapped onto face areas • face stimulated, phenomenological experience was sensation in the ‘phantom’ limb.

(Ramachandran, Rogers-Ramachandran and Stewart, 1992)

Does vision play a role in touch perception? George Berkeley (1685-1753)

“My Design is … to consider the Difference there is betwixt the Ideas of Sight and Touch, and whether there be any Idea common to both senses.”

An Essay towards A New Theory of Vision (1709)

Does vision play a role in tactile acuity? • Does viewing the body enhance the sense of touch?

– Studies by Patrick Haggard and colleagues

• Whiteley L, Kennett S, Taylor-Clarke M, Haggard P. 2004, Perception • Taylor-Clarke M, Kennett S, Haggard P., 2004, Neuroscience Letters • Press C, Taylor-Clarke M, Kennett S, Haggard P., 2003, Exp. Brain Research • Haggard P, Taylor-Clarke M, Kennett S. Curr Biol. 2003 • Kennett S, Taylor-Clarke M, Haggard P. 2001, Current Biology

Results Seeing arm significantly reduced the 2 point threshold. Seeing arm under magnifying glass reduced the threshold further.

Social Cognitive Neuroscience 2PDT on back of hand

Seeing arm of another person also reduces the 2 point threshold

How are objects recognised through touch?

• Problem: – During object exploration, different regions of skin and hand are stimulated – Different kinds of information can stimulate different regions

• How then, do we perceive a single, coherent object?

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Receptive fields of neurons in S2

• Answer: – Information is integrated from across different stimulated sites on the skin – Basic geometric structures are detected (e.g. edges) and grouped together

– Evidence for large receptive fields of neurons in S2 which help integrate information across different tactile sites

• Fitzgerald, Lane, Thakur & Hsiao (2006 a and b). Journal of Neuroscience.

• For a review see Haggard, P (2006). Sensory Neuroscience: from skin to object in the somatosensory cortex. Current Biology, 24;16, 20

Tactile object recognition • Haptics = active touch

• J.J. Gibson (1962) – Active better than passive touch – ‘Cookie’ cutter experiments

• Lederman & Klatzky (1987) – Different exploratory procedures involved in different haptic tasks

Tactile object recognition • Exploratory procedures optimise information pick-up for a specific task

– Susan Lederman & Roberta Kaltzky (1987)

Visuo-tactile object recognition • Object information can be shared across vision and touch for

recognition

• touch provides information about the back of objects to enhance recognition (Newell, Ernst, Tjan & Bülthoff, 2001)

• object recognition in one modality can be primed by object previously presented in other modality

(Reales & Ballesteros, ‘99)

• Object recognition improves when information from all modalities is present simultaneously

(Giard & Peronnet, ‘99; Newell, Ernst, & Bülthoff, 04)

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How is tactile and visual information combined? Candidate models for integration:

Maximum likelihood estimate (MLE) model Crossmodal informaiton is integrated in statistically optimal way

(Ernst & Banks, ‘01 - behavioural evidence)

Tactile information is recoded to visual information via visual imagery (Prather & Sathian, 2004 - neuroimaging evidence)

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