The Body In Space The Body In Space (a “constructed” modality)

How are our limbs, trunk, and head positioned?

Where is our body with respect to the world?

Where are objects with respect to our bodies?

Where are objects with respect to each other? X-centric

• Egocentric – with respect to the perceiver • Allocentric – with respect to some external reference (“the world”) • Retinocentric – eye centered • Head centered, etc…

“frames of reference” or “coordinate frames” sense of space Definitions proprioception: the perception by an animal of stimuli relating to its own position, posture, equilibrium, or internal condition. proprioceptor: sensory receptor, found chiefly in muscles, tendons, joints, and the inner ear, that detects the motion or position of the body or a limb by responding to stimuli arising within the organism. Two systems that use position sense

• Dorsal Column / • Cerebellum Medial Lemniscus • position sense • motor coordination (and locomotion) • “conscious” • “unconscious”

Ataxia: unsteady and clumsy movement of the limbs or trunk due to a failure of the gross coordination of muscle movements disorder: disorder: sensory ataxia cerebellar ataxia DC/ML System Dorsal Column/Medial Lemniscus Responses of VPL neuron to

Tuning kneeof VP thalamic angle neurons to joint angle of the knee

From where do these signals come? Joint Position Sense

• Two observations: – Constant tug on tendons seemed to have no perceptual effect – Anesthetizing finger joints interrupted position sense • Led to incorrect conclusion that joint receptors must be responsible for conscious proprioception Synovial joint (freely moveable) Joint Receptors Are Not the Whole Story

• Joint receptors primarily discharge at extremes • When joints are totally replaced by prostheses, joint position sense is still available • Muscle spindle inputs do contribute to our position sense, but they must be appropriately stimulated • Vibration of the tendon activates Ia afferents, which leads to a sensation of limb position change • Large diameter afferents project (via the DC/ML path) to area 3a of sensory cortex

Muscle Spindles & Golgi Tendon Organs

monitor muscle length monitor muscle tension Joint angle perception

Ferrell et al. Responses of VPL neuron to

Tuning kneeof VP thalamic angle neurons to joint angle of the knee

Phasic response component

Sustained response component •Dorsal root section (dorsal rhizotomy) eliminates incoming sensory information from the limb

•How can a deafferented limb be used if it cannot be directly sensed?

X Efference Copy Coordinate System Transformations

• Points in space can be referenced to many different coordinate systems – eye (eye-centered/oculocentric, retina/retinocentric) – head (craniocentric; audition & vestibular) – body (egocentric) – world (allocentric) • As we plan movements, information coded in various coordinate systems must be unified Coordinate System Transformations Parietal cortex

Eye position Eye-centered coordinates Neck proprioception Head-centered coordinates Vestibular information Body-centered coordinates Visual information World-centered coordinates

Auditory information

Evidence? Andersen & Mountcastle, 1983

Anderson experiment 40 imp/sec 40 Stimulus Stimulus

Gaze Position

Retina Nature Neuroscience - 9, 1337 - 1343 (2006) A human parietal face area contains aligned head-centered visual and tactile maps Martin I Sereno & Ruey-Song Huang Somatosensory (air puff)

Visual

Aligned somatosensory and visual maps for a single subject Sensing “Space”

stereognosis: recognition of objects through tactile exploration (proprioception, somatic sensation, temperature) astereognosis: loss of the ability to recognize objects by touch Anterior Parietal Cortex Primary somatosensory deficits

• Decreased somatosensory sensitivity • Sensory ataxia (“afferent paresis”) • Other perceptual disorders – astereognosis – asomatognosia – loss of a sense of one’s body – finger agnosia – inability to point/identify fingers Anterior Posterior Parietal Parietal Cortex Cortex

Posterior Parietal Cortex

• receives projections from primary somatosensory cortex (S1) • also receives projections from visual and auditory cortices, thalamus, and hippocampus: association cortex More complex parietal deficits • Balint’s syndrome (areas 5/7) – “sticky fixation” – simultagnosia – can only attend to one item at a time – optic ataxia – difficulty reaching for objects using vision • Contralateral neglect (right parietal) • Apraxias – loss of skilled movements (in absence of impaired primary motor function) – Ideomotor apraxia – inability to copy movements or gestures – Constructional apraxia – impairment in assembling, building, drawing objects, copy figures Hemi-neglect Impairments in “constructional ability” (constructional praxis): Ask patient to draw or copy line figures

Rey-Osterrieth Complex Figure Test

Ideomotor/Ideational apraxia: Perform simple/complex series of movements comb your hair/unlock a door, open it, walk through R

“Dressing apraxia” – difficulty performing the spatial arrangement of clothing with respect to the body axis Blanke et al., Nature, 2002