Lecture 22: Locomotion Locomotion is an activity leading to a change in the location of the body in external space. Examples: walking, running, hopping, swimming, flying, crawling, etc. Important characteristics:  Velocity  Stride length  Relation between the support and swing phases  Relative timing of the extremities (gait)

Locomotion: EMG Patterns During Human Walking

Locomotion in Different Preparations

Locomotion Induced by Stimulation of MLR

Effects of Changing the Stimulation Strength

The Locomotor Region and Strip

Experiments on Decerebrate and Spinal Animals  Electrical stimulation of certain brain (and spinal) areas can induce locomotion.  Gait changes with the strength of the stimulation.  Locomotion and gait changes can also be induced by treadmill motion and by intraspinal drugs (GABA).  Fictive locomotion can be seen.

 The spinal cord is likely to contain one, two, or even four Central Pattern Generators (CPGs).  A CPG can be driven by descending and ascending signals.  It does not necessarily require either signal.  It can produce different gaits. Graham Brown versus Sherrington: Experiments on Decerebrate and Spinal Animals

Central Pattern Generator (CPG)  A CPG is a hypothetical structure in the central nervous system that can generate patterned (rhythmical) activity.  It can be driven by “higher” centers as well as by peripheral information.  Both sources of information can lead to gait changes.

Homunculus A Simple Two-Half-Centers CPG

CPG “Higher centers”Afferents  -motoneurons Central Pattern Generator

CPG in the Lamprey Has Been Mostly Deciphered

CPG in Humans: Starting Induced Locomotion

CPG in Humans: Aftereffects of Spinal Stimulation

CPG in Humans: Different Effects of Spinal Stimulation INTERLIMB COORDINATION RHYTHMIC LEG MOVEMENTS WITH LOCOMOTOR SIGNS TYPICALATYPICAL CYCLE STRUCTURE ASYMMETRIC CYCLES OF LEFT AND RIGHT LEGS INCOMPLETE CYCLE STEPPING WALK-LIKE RUN-LIKE UNILATERAL STEPS IN-PHASE STEPS DIFFERENT FREQUENCIES IN THE TWO LEGS BILATERAL STEPS UNUSUAL COORDINATION BETWEEN MOVEMENTS IN PROXIMAL AND DISTAL JOINTS ALTERNATING BETWEEN A FEW STEP CYCLES OF ONE LEG AND THE OTHER LEG

CPG in Humans: Effects of Perturbations

CPGs in Humans: A Hypothetical Structure

Surface Stim AB Preprogrammed Reactions in Locomotion

Corrective stumbling reaction:  Occurs during locomotion  Can be induced by a mechanical stimulus to the foot  Represents a complex pattern of EMG changes  Leads to a quick step over the obstacle Preprogrammed Reactions in Locomotion

Gait in Locomotion Relative timing: a programmed feature versus an emergent property

WalkingTrottingGalloping Gaits in Quadrupeds

Relative Timing: Motor Programming

Relative Timing: Dynamic Systems

Relative Timing: Control + Coordination

Preparation for Stepping