Strick Lecture 1 March 22, 2006 Page 1

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1 Strick Lecture 1 March 22, 2006 Page 1 Motor Planning and Programming The point of this lecture is to reveal important features about the operation of our motor system by studying motor behavior. Figures (4): 1 (Triphasic), 2 (Simple reaction time), 3 (Sequential Movement), 4 (Apraxia Lesion) Lecture Outline I. 1st Video Tape Segment: Robotic Arm mixing a drink- What tasks does the nervous system perform when we move? II. III. Presentation of the "Triphasic" pattern of muscle activity associated with the performance of 'Step-tracking' movements- This demonstration illustrates that even simple movements of a single joint are generated by a complex set of central commands. (Figure 1) 1st Demonstration: Paper Money and Ruler Drop- Simple and Choice Reaction Time. The processing of simple movements. This demonstration illustrates that the Motor System is constructed from chains of interconnected neurons. (Figure 2) IV. 2nd Video Tape Segment: Sugar Ray- Hitting a speed bag; Sparring. Illustrations of: a) motor programming (we do not perform all of our movements as reaction time movements) and b) the consequences of reaction time. V. Presentation of Sequential Movements- Motor processing during the execution phase of movement. (Figure 3) VI. VII. VIII. 2nd Demonstration: Asymmetrical or Decoupled Jumping Jacks- How easy is it to acquire and retain a motor skill? 3rd Video Tape Segment: Apraxia = a disorder of skilled movement. What happens when motor programming is disrupted? 4th Video Tape Segment: The use of muscle activity to drive a prosthetic hand = A clinical application of neuroscience principles.

2 Strick Lecture 1 March 22, 2006 Page 2 Introduction- I want to provide you with a novel perspective about the control of movement. I am going to illustrate some important features of the operation of our motor system by examining motor behavior. I. 1st video tape- Robotic arm mixing and pouring a drink. Let's start by looking at a videotape segment of a Robotic Arm preparing a Martini. I would like you to define and keep track of the different motor tasks which the arm has been programmed to perform. 1) The robotic arm reaches to different points in space 2) The arm grasps objects of different size and weight- this requires it to adjust grip force for different objects 3) The arm performs different motions- it pours, it stirs and it strikes a match It is clearly a very complicated task to program this mechanical device to perform all of these functions. Your arm is capable of performing all of these feats. What does this say about the programming of movement that is performed by the central nervous system? In many respects we take the accomplishments of our motor system for granted. II. Presentation of triphasic EMG and step-tracking movements- The generation of even relatively 'simple' movements (e.g., of a single joint) is a remarkably complex task. The muscle activity which occurs when you flex or extend your wrist provides some insights into the task performed by the nervous system when it generates movement. (Figure 1) The figure illustrates: 1. Huffschmidt Phenomenon The first event that occurs in this simple movement is a decrease in activity in the antagonist muscle. It makes sense that the first task the nervous system would perform when it generates a movement is to turn off the activity in muscles that would oppose the movement. This is called the Huffschmidt phenomenon. 2. Agonist activity = 2 bursts separated by a silent period. The first agonist burst occurs for a limited period of time (less than 100 msec.) and then, the agonist muscle is relatively silent during the remainder of the movement's initial trajectory. The pulse of force that the agonist generates is very much like the ballistic pulse of force generated by a bat hitting a ball. 3. Electro-mechanical Delay Note that movement doesn't start at the same time that muscle activity begins. There is an electro-mechanical delay between the onset of activity in an agonist muscle and the onset of movement. 4. The antagonist burst occurs at or just after movement onset. Two important questions about this burst of muscle activity:

3 Strick Lecture 1 March 22, 2006 Page 3 - Question 1) What is the function of the antagonist burst? Why would you turn on a muscle that acts to oppose movement at or just after the movement has begun? Ans.: The burst functions as a 'brake' to terminate movement and reduce overshoot. It is very similar to the brake of a car which is applied well before you reach a stop sign in order to bring the car to rest at the stop sign. - Question 2) How is this burst generated? a) Is it a reflex generated by stretch receptors in the antagonist muscle or b) Is it generated by central mechanisms? Ans.: There is considerable evidence that the antagonist burst is centrally generated. 3 Pieces of Evidence for the Central Generation of the Antagonist burst 1. TIMING- The antagonist burst begins very early in a movement. There is not enough time for feedback to generate this muscle activity. 2. DEAFFERENTED PATIENT- The antagonist burst is present in patients with a pan-sensory neuropathy (no deep tendon reflexes, little subjective appreciation of touch, pain, temperature, position or vibration, i.e., essentially deafferented). Thus, the burst is present when there is no afferent feedback. 3. CONTROL BY STRATEGY- If a normal subject is asked to accurately terminate his movement, the burst is present. If, however, the subject does not attempt to be accurate or allows the movement to be terminated by a mechanical stop, the antagonist burst is absent. Thus, the burst depends on the intent of the subject. All of what we have just described about agonist and antagonist muscle activity makes intuitive sense. However, when you decide to move, you don't intentionally generate this pattern of muscle activity. The pattern is something your motor system generates for you. Thus, even when you intend to perform a 'simple' movement like flexing or extending the wrist, your motor system performs a task of remarkable complexity. III. Demonstration: Measurement of reaction time. (Figure 2) The study of simple movements also can be used to illustrate 2 important principles: 1) Movement is generated by circuits of neurons. 2) Circuits of neurons take time to process information. Objects fall a distance = _ at 2 ; a = 32 ft/sec 2

4 Strick Lecture 1 March 22, 2006 Page 4 Note: 1) The minimum reaction time between the appearance of a visual stimulus and the onset of electrical activity in muscle = 100 msec. 2) The delay between the onset of electrical activity in muscle and the production of force (electro-mechanical delay) = approximately 50 msec Thus, the minimum delay between the onset of a visual stimulus and the production of force = = 150 msec. 1. Simple reaction time- The principle of motor circuits. Why is there a delay between the occurrence of a stimulus and your response? The brain is composed of nerve cells. Because of this feature, there are at least 3 different delays built into the system. Ans.: 3 delays built in to the motor system a. Axonal Conduction Delays: Nerve cells have axons which take time to conduct information = conduction delay. Thin axons conduct more slowly. The longer the axon, the greater time it takes for an axon potential to travel from the cell body to the synapse. Because of the different distances involved, the reaction time for your foot to move is longer than the reaction time for your mouth. b. Synaptic Delays: Nerve cells also communicate at specialized sites called synapses. At these points the electrical activity of the nerve axon causes some special chemicals to be released. The process of electro-chemical transmission results in an additional delay termed a synaptic delay. As the number of neurons involved in a circuit grows, so does the number of synapses involved. As the number of synapses increases, the delay caused by the circuit becomes longer. c. There is an electro-mechanical delay between the signal to muscle and the onset of force production 2. Choice reaction time- DROP TWO RULERS Why does reaction time increase when the number of choices is increased? Ans.: In the choice task a. you can't prepare a response in advance b. sense, decide and select: your nervous system must decide which trigger signal occurred and select which response to perform c. as the task becomes more complex, the circuitry necessary to perform the task becomes more complex (i.e., more neurons with synaptic delays) The more complicated the task, the more complicated the neural circuit. In the simple reaction time task the subject can prepare a motor response in advance. Then, the visual stimulus of the yardstick dropping triggers the response. In the choice reaction time task the subject cannot prepare a single motor response in advance. Instead the subject must make a decision based on the visual input. This process of making a decision requires more

5 Strick Lecture 1 March 22, 2006 Page 5 complicated circuits (involving more neurons and synapses) and thus, requires additional time for processing. What would happen if you always required a stimulus to trigger every movement? What would happen if you could only perform one movement at a time and then had to wait a reaction time to be able to trigger the next movement? Imagine how slow you would be at typing or how long it would take to write a sentence. If each movement in writing a simple word were performed as part of a reaction time task, you would pause after each letter. Clearly, the brain's ability to string together simple movements to perform complicated tasks is very important. This process is called motor programming. IV. 2nd video tape- Sugar Ray. Segments of video tape which illustrate some examples of motor programs and how they improve the speed of performance. 1st Boxing Segment This is a short workout on the Speed Bag. The number in the frame changes every 30th of a sec or every 33 msec. It is a simple repetitive movement that requires great timing and accuracy. At this speed it is very difficult to see the actual movements of the bag. You can see that a boxer can't perform this as a reaction time task. This sequence of movements will be shown again, but in this case the tape speed is slowed to one tenth its normal speed. The boxer hits the bag every 300 msec. The bag travels from one side to the other in under 100 msec. Sugar Ray hits the bag msec after it has touched the far side. The variation in the timing of each sequence is no more than msec. These times should make it clear to you that a boxer cannot hit the speed bag if he is trying to do it as a reaction time task. The bag travels from one side to the other faster than you can react! 2nd Boxing Segment This next segment of tape is part of a sparring session. Shortly you will see Sugar Ray throw a combination of 4 punches. This sequence will be shown twice at normal speed and then, twice at reduced speed. The 4 punches are thrown in under 700 msec. The time between the right to the head and the last left is 231 msec. The time for the last punch to travel from Leonard's shoulder to Odell's jaw is 170 msec.

6 Strick Lecture 1 March 22, 2006 Page 6 Principles illustrated in the videotape segment: 1. Reaction time- Because the last punch travels from Leonard's shoulder to Odell's jaw in under a reaction time, even if Odell sees the punch coming he can't react in time to do anything about it. 2. Motor programming- Notice that there is no pause between each punch in the combination. In this sequence the punches are thrown smoothly one after another. Thus, Leonard has decided in advance to throw a whole sequence of punches and preprogrammed that sequence. V. SEQUENTIAL MOVEMENTS- (Figure 3) Let's take another example of motor programming and analyze it in some detail. This example involves the storage, recall and unloading of sequential movements. So far we have talked about the motor programming which occurs in the period when a subject is preparing to move. There is also evidence that motor processing occurs during the actual execution of a movement. Basic observation: The reaction time to perform the first element in a sequence of movements increases as the length of the sequence increases. The amount of increase is between msec for each element. This is called the sequence length effect. It has been observed in typing, speech and piano playing. Typing example: "a", "an", "and", "andy" Explanation of the effect: There appear to be two phases in the initial processing of sequential movements: 1st phase occurs during the Instruction period - this is when the sequence is stored. 2nd phase occurs during the Execution period - this is when the sequence is unloaded and executed. It takes more time to unload longer sequences than to unload shorter sequences. The unloading process isn't completed until after the onset of the 'GO' signal. VI. 2nd Demonstration: Asymmetrical or Decoupled Jumping Jacks Let's look at another aspect of motor programming. How easy is it to acquire new programs? (e.g., Asymmetrical Jumping Jacks) What occurs in the central nervous system when we acquire new skills. What occurs in order for us to retain these skills?

7 Strick Lecture 1 March 22, 2006 Page 7 VII. Apraxia: What happens if the part of the brain which is involved in programming movements is damaged? (Figure 4) The result is a syndrome termed Apraxia = a disorder of skilled movements. Simple movements are largely normal (although somewhat clumsy). The deficits in movement seen in patients with apraxia cannot be explained by changes in tone or any other abnormal movement syndrome (e.g., cerebellar or basal ganglia disorder). In tests for apraxia subjects are asked to: 1. Respond to verbal commands- demonstrate that they understand commands. 2. Imitate examiner. 3. Perform non-representational movements (i.e., meaningless movements like positioning the limb in space). 4. Perform representational movements (pantomime combing hair, brushing teeth, etc.). The subject will be asked to perform with and without meaningful objects [i.e., brush]. Performance will often improve when the object is present. Non-representational Hand Movements: 1. Hand to forehead 2. Finger to ear- note misplacement 3. Hand to back of head 4. Thumb to forehead- note poor hand posture Representational Movements: 1. Salute- note S performs the same movement as previous trial = motor perseveration 2. Wave goodbye 3. Scratching head 4. Blowing a kiss- note the sequencing problem sequence = a) flat hand to mouth, b) tilt of hand, c) blow across hand 5. Snap fingers 6. Brushing teeth- note twist instead of back and forth motion 7. Shaving- note that hand goes to the mouth first, while examiner goes to ear and ends at chin 8. Comb hair- note patient again starts at his mouth, adds shaving and then adds movement around ear 9. Writing signature 10. Flipping a coin- note that the subject goes back to the prior writing motion

8 Strick Lecture 1 March 22, 2006 Page 8 The analysis of movement and muscle activity has some practical applications. For example, the next segment of video tape will show how the electrical signals recorded from muscles can be used to drive artificial limbs. Major points in lecture: 1. Even movements about a single joint are associated with a complex pattern of muscle activity. 2. It takes time to generate a motor response. The reason it takes time is because responses are generated by circuits of neurons. 3. Our ability to perform skilled movements depends on stringing together simple responses into sequences of movements. 4. Finally, it is possible to have lesions of the nervous system which damage our ability to generate sequences of movements, but leave intact our ability to generate the simple Figure 1

9 Strick Lecture 1 March 22, 2006 Page 9 Figure 2 Figure 3

10 Strick Lecture 1 March 22, 2006 Page 10 Figure 4