Lateral view of human brain! Cortical processing of touch!

Lateral view of human brain! Cortical processing of touch!

How do we perceive objects held in the hand?! Touch receptors deconstruct objects to detect local features! Information is transmitted in parallel from populations of touch receptors in the fingers and palm to the CNS! Central pathways merge information from neighboring receptive fields at each synapse! Cortical networks use inhibition to distinguish object edges from areas of uniform curvature and texture! Hand movements enable different groups of receptors to sample the same object features! Memories of previous experience enable object recognition and classification!

Touch fibers innervate small regions of skin! Johansson RS, Vallbo ÅB. Trends Neurosci 1983

Cortical neurons integrate multiple receptor inputs! Georges Seurat, A Sunday on La Grande Jatte -- 1884-86, Art Institute of Chicago!

Central projections of touch fibers in the spinal cord!

Touch is relayed in the dorsal columns to the cortex!

Convergence integrates inputs of adjacent receptors! A! B Convergence from same receptor class (modality)! Receptors that are stimulated together wire together! Convergence pattern selects stimulus features (edge orientation)!

Somatosensory areas of the cerebral cortex!

Minicolumns of neurons span the cerebral cortex! Jones EG (2000) PNAS 97: 5019-5021

Information is processed in columns of cortical neurons!

Receptive fields in a cortical column overlap! Mountcastle VB, J Neurophysiol 1957!

Cortical columns are arranged topographically!

Orderly maps of the body in the brain (homunculus)!

Dermatomes represent the body in the spinal cord!

Brain maps reflect innervation density! Kaas JH, et al. 2008

Optical imaging of brain maps in monkeys! Shoham D, Grinvald A. J Neurosci 2001

Median nerve cut silences part of S-I cortex! Merzenich MM, et al. Neuroscience 1983!

New receptive fields 4 hours after nerve cut! Merzenich MM et al. Neuroscience 1983!

New hand representation in S-I after median nerve cut! Merzenich MM et al. Neurosci 1983b!

Dorsal rhizotomy (C5-C8) impairs hand function! Darian-Smith C, Ciferri MM. J Comp Neurol 2005.!

Cortical maps reorganize following peripheral lesions! et al. Science 252: 1857-60 1991

Amputees experience phantom sensations!

Cortex reorganizes in amputees!

Trigeminal fibers sprout after a dorsal column lesion! Jain N et al. PNAS 2000;97:5546-5550

Learning alters brain maps!

Training focuses and enhances cortical activity! Lotze M, et al. NeuroImage 20:1817 1829 (2003)

Maps of whiskers in rodent S-I cortex called barrels!

Complex neural interactions within cortical columns! Brecht M. (2007) Curr Opin Neurobiol 17: 408-416

Map plasticity in rodent barrel cortex!

Hierarchical projections to and from S-I cortex!

Cortical receptive fields enlarge at each synapse!

Convergence integrates inputs of adjacent receptors! A! B Convergence from same receptor class (modality)! Receptors that are stimulated together wire together! Convergence pattern selects stimulus features (edge orientation)!

Orientation selective neuron (Area 2)! Hyvärinen J, Poranen A. J Physiol 1978

Inhibition extracts important features! A! B! Winner-take-all sharpening of strongest inputs (feedback inhibition)! Order of receptor stimulation determines output (lateral inhibition)! Higher areas can control ascending output (descending inhibition)!

Direction sensitive neurons (Area 2)! Gardner EP, Costanzo RM. J Neurophysiol 1981

Stimulus context alters cortical responses! Sripati AP, et al. J Neurosci 2006

Convergence patterns enable feature detection!

Information Processing in Cerebral Cortex! Bottom up: Receptors encode stimuli! 1. What: the sensory modality! 2. Where: position in space or body! 3. Intensity: stimulus amplitude! 4. Duration: persistence or adaptation! Top down: Information interpreted in context! 1. Memory: previous encounters and learning! 2. Attention: selection of features relevant to task! 3. Circuitry: structure of pathways and synapses! 4. Motivation: emotional connotation!

Attention modulates S-II responses! Hsiao SS, et al. Behav Brain Res 2002!

S-II integrates sensory and learned responses! Romo R, et al. Nature Neurosci 2002!

Active and passive touch! S-I cortex! S-II cortex! Hinkley LB, et al. J Neurophysiol 2007!

Active and passive touch of whiskers in rodent cortex! Touch cells! Whisking cells! Szwed et al. Neuron 2003!

Mechanoreceptors sense hand actions! Westling G, Johansson RS. Exp Brain Res 1987

SI neurons respond to hand contact with objects!

Cortical circuits for reaching and grasping! Gardner EP, et al. J Neurophysiol 2007!

PPC neurons respond before touch! Spikes per sec 40 30 20 II IIIIII I I III I IIIIIII II II I I I I II III I I II I I I I I I I I I I I I I III I IIII I II I I I I I I I I I I I I I III I I IIIIIII I I I I I I I IIIII I I I III I IIII I I I I I I I I I I I I I I I I I I I I I I I IIII II I III I IIIIII I I I I III I I IIII I I I I I I I I I I I I I II II I IIIIIIIII I I IIIIII I II I II I I I I I I I I II I I I I I I I II III II II III IIIII I I II II I I I I I I II I I II III I I I I II I I I I III II I I I I II I I I I I I I I I II I I I II I I II II I II I I I I I I I I I I I IIIIIIII I I I IIII II I I I I I I I I I I I I I III I I I I I I I I IIIII I I II II II I I I I III IIIIII III IIII III I I II I I I II I I I II I I I I I I I I I I I I I I I IIIII IIIII II I I I I I II II II I I I II I II I I I I II I II III I IIII II III II IIII I III I I II I II I I II I I I II III I II I II I I I III II I I I III I I I III I II II IIIII II II II I III I III I II IIIIII I III IIIII I I II I II I I I IIIII I IIIIIIII III I II I I I I I I III I I I II I I I I II I I I I I II I II II II IIIIII I I I I I III I I I I II I I I I I I I I I I II I III I I I I I I I II II IIII III I I I I I I I II I I I I I I III III I I I II I II I III III I II I I I II II I I I I I I I I II I II II II I I I I IIII II II I II I II II II I I II I IIII II II I I II I I I I I III II I I I I I I I I IIII II I I I I I I II I II III I II I I II I I III III I I I I I I I II I II II I II III I I I II I II I II I II I I III I I II I I I I I I I II II I I I III I I I I I II II I I III II I I III I II I I I I I I II I I III II IIIII III I I I II I I I I I I II I I I I II IIII I III I I I III I I I I I I I I II I II I II I IIII I I I I II I I I II I I III I II I I I I II I II I II I III I II IIIIII I III III I I I I I I I I I I I I I I I I I I I I I I l l l l l l l l l l Previous Approach Contact Grasp Lift Hold Lower Relax Release Next Unit H17094-131-3.2 N = 224 trials 10 0-1000 -750-500 -250 0 250 500 750 1000 1250 1500 1750 2000 2250 2500 2750 3000 Time re contact (ms)

Neural responses reflect approach style!

Area AIP (BA7) neurons code hand posture!

MI neuron excited by reach and inhibited by grasp!

Some MI neurons respond to actions of both hands! Contralateral! (left)! Ipsilateral! (right)!

Area 2 inactivation produces clumsy grasp! Hikosawa O, et al. J Neurophysiol 1985!

S-I Cortical Lesions Impair Touch! Loss of touch sensation in lesioned area! Impaired two-point discrimination! Poor texture discrimination! Loss of stereognosis! Localized to specific body region in the map! Impaired motor function especially hand! Clumsy grasping! Poor motor coordination!

Neurological tests of touch sensation! Simple somatosensory! Touch threshold! Two-point discrimination! Vibration sense! Position sense of index finger! Complex tactile recognition! Texture discrimination! Form recognition (stereognosis)! Size discrimination!

Parietal lobe sensorimotor deficits in 9 patients! Pause M, et al. Brain 1989!

Neurological tests of active touch! Hand position and force control! Grip force! Rhythmic tapping! Reach to a target! Exploratory and skilled movements! Insertion of pegs in slots! Precision (pincer) grip of small objects! Exploratory movements when palpating objects!