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 centersAfferents -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