Rhythmic Auditory Stimulation(RAS)

Developed primarily by Thaut, McIntosh, & Rice at the CBRM at Colorado State University

NMT technique utilizing the physiological effects of rhythm on the motor system to increase the efficiency of controlled movement patterns during rehabilitation.

Enhancement of gait is mediated by an entrainment effect where movement frequencies and motor programs entrain to rhythm through anticipatory cuing of functional movement patterns.

RAS Uses

Immediate entrainment stimulus providing rhythmic cues during movement.

Listen to music with strong rhythmic pulse while walking to enhance walking tempo, balance, and control of muscles and limbs.

Stimulus for training where patients train with RAS for a prescribed period of time in order to achieve more functional gait patterns which they then transfer to walking without rhythmic facilitation.

Mechanisms

Rhythmic Entrainment Priming of the Auditory Pathway Cuing of the Movement Period Step-Wise Limit Cycle Entrainment

Rhythmic Entrainment

Physiological basis for the perception of rhythm is the detection of periodicity patterns in amplitude modulations of sound

External rhythm serves as an external oscillator which has a “magnet” effect on one’s internal timekeeper.

Strength of the effect is substantiated by the observation that motor responses can be entrained by rhythmic patterns even at levels that are imperceptible.

Auditory-Spinal Facilitation

Physiological entrainment of muscle activation through rhythm perception takes place via reticulospinal pathways.

Neurons in the spinal cord become excited as a result of auditory perception.

Support for these concepts were observed in research when many components of the neural synchronization network were already activated and “entrained” simply by listening to rhythm.

One result of neuronal excitement is the “priming” or “readying” of muscle groups utilized in movement, which has a facilitative effect on subsequent motor functioning.

Cuing of the Movement Period

Period Synchronization - adaptation of the movement duration to the rhythmic stimulus duration

Phase Synchronization - ISI and IRI are closely matched although period synchronization is not behaviorally observable.

Kinematic models show that period (or frequency) entrainment results in enhanced kinematic stability through the stabilization of the following parameters: acceleration, velocity, trajectory).

Step-Wise Limit Cycle Entrainment(SLICE)

RAS frequencies (tempi) need to be set initially at a pt.s ‘resonant’ (current or intrinsic) frequency of movement.

Limit cycles are frequencies at which any moving system performs optimally (developed in the fields of engineering, physics)

Hence, RAS frequencies should be adapted to a person’s current limit cycle, i.e. the current step cadence.

SLICE cont’d

Initial purpose of RAS is to stabilize movement parameters at a pt.s current limit-cycle.

New limit cycles can be gradually entrained through a step-wide incremental process to approximate a pt.s pre-morbid limit-cycle.

Ex. When using RAS to increase cadence of PD pt.s, stride lengths will increase also due to the mechanical properties of the gait generating system.

SLICE cont’d

In the case of pt. who has a nearly normal cadence with shortened stride length, RAS is used to match the current cadence or a slightly slower one in order to increase stride length through added kinematic stability which is present due to the entrainment process.

SLICE - most commonly used RAS protocol in the treatment of gait disorders.

RAS Gait Training Procedures

Assessment Resonant Frequency Entrainment Frequency Modulation Advanced Adaptive Gait Fading Reassessment

Cadence Assessment

Cadence - steps/minute Client walks for 60 seconds while you

count each step; walks for 30 seconds then multiply steps by 2)

This is unaccompanied by music. Avg. cadence for an adult is 105-120

steps/min but is age related.

Velocity Assessment Velocity - Meters/minute or feet/minute Measure distance across time Pt. walks for 60 seconds and you measure how

many meters or feet they walked (multiply by 2 if walking for only 30 seconds)

Difficult to do because of space limitations. Hospitals usually have 1-foot floor tiles. Count

the tiles to get a feet/min measurement, then divide by 3.281 for meters/min (1 meter = 3.281 ft.)

Velocity Assessment cont’d

Measure off 10 meters on the floor. Time the number of seconds it takes a pt. to walk 10

meters. *Have them start a few ft. before and continue going for a few ft. past the line.

Divide the number of seconds by 60 (60 sec/min) Divide 10 meters by the number of minutes which gives

you the meters/minute value. Ex. Pt. walks 10 meters in 7 seconds 7 sec/60 sec/min = .117 minutes 10 meters/.117 minutes = 85.5 meters/minute Avg. normal velocity in adults is 80 m/m, but is age

dependent.

Stride Length

Divide velocity by cadence. This will provide the number of meters for each

step. (*This in inaccurate if there is uneven step length between the right and left legs)

Multiply this figure by 2 and this will give you the average stride length.

Ex. 70 meters/min (velocity) / 80 steps/min (cadence) = .875 meters/step

.875 meters/step x 2 steps/stride = 1.75 meters avg. stride length.

Step 2 Resonant Frequency Entrainment

Match RAS frequency (music tempo) to gait cadence and walk with patient.

Pt.s who are not ready for sustained walking exercises can practice specific pre-gait exercises, e.g. weight shifting - front to back, side to side, etc. 6/8 tempo usually more preferable

Therapist may need to cue proper gait mechanics, e.g. stride length, arm swing, posture, toe clearance, heel strike, etc.

Step 3 Frequency Modulation Increase tempo by no less than 5% ~ an increase that still

allows them to maintain proper mechanics. Again use verbal cues, but feedback should be kept to a

minimum as you may interfere with rhythm perception and its subsequent effects

Clients who have attention problems may need enhancing verbal cues initially, e.g. left-right, 1-2

Generally, frequencies (tempi) that are more closely aligned with a pt.s pre-morbid state tend to more have the strongest effect on overall gait patterns.

In some cases, a deceleration in RAS frequency is indicated for pt. groups who have the proclivity for unsafe walking patterns.

Considerations

2/4 or 4/4 meter with strong beat accents (1 & 3) If a pt. utilizes an assistive device, cane or

walker, a 3-step pattern may be more useful, e.g. step, step, walker

The motivational quality of music is a bonus secondary effect ~ client preferences. Note that some diagnoses do not perceive complex acoustic patterns well so very simple music or simply a metronomic click would work best.