J Physiol ; : In addition to the proximal to distal mechanoreceptor density gradient from palm to finger tip, differences were also noted across finger tips. The highest concentration of mechanoreceptors is found on the index and middle fingers versus the thumb and radial half of the ring finger.
Consequently, the higher density of mechanoreceptor units in the first and second finger tips may allow these fingers to be more suitable for SMP. The receptive field of a mechanoreceptor corresponds to that region of the skin or subcutaneous tissue that is innervated by the terminals of the receptor and the surrounding tissue conducting the stimulus to the receptor.
The size of the receptor field determines the ability of the receptors to discriminate spatial details. As a result, Meissner corpuscles and Merkel receptors on the fingers can resolve fine spatial differences. Pacinian and Ruffini corpuscles can only detect coarse spatial differences. Therefore, with respect to SMP, the smaller receptor fields of the Meissner corpuscles and Merkel receptors are more discriminatory for the recognition of the subtle spatial changes incurred by vertebral motion testing.
In the brain, the cortical area representing the fingers is greater than the palm. Consequently, the size of the receptive field and its cortical representation are inversely related. Sensory discrimination, quantified by measuring two-point discrimination thresholds, varies throughout the body. As a result, the greatest capacity for sensory discrimination resides in the fingertips where there is the highest density of mechanoreceptors, the smallest receptive fields, and the greatest cortical representation.
The detection of a movement stimulus is a primary function of higher cortical neuronal activity within areas 1, 2, and 3 of the somatosensory cortex. The role of our somatosensory cortex in the manual detection and coding of various movement activity demonstrates the importance of trusting our sensory perceptions of movement rather than critically analyzing the motion event by overutilization of the associative areas in the prefrontal cortex.
Touch perception should, therefore, involve a primary feeling process and not a primary thought process. Both educators of manual therapy and students should be aware that excessive prefrontal cortex critical analysis during SMP may actually interfere with accurate identification of the movement event given that central processing of the movement occurs within the somatosensory cortex. Each of the four regions of the primary somatic sensory cortex receives input from all areas of the body surface.
Area 1 receives input from the rapidly adapting cutaneous receptors and respective neurons whereas area 2 obtains input from the deep pressure receptors. In one study involving the fingers of awake monkeys, the pressure detecting Pacinian corpuscles in the subcutaneous region did not transmit an exact signal of a sensory stimulus. In contrast, the slow adapting Merkel and rapid adapting Meissner touch receptors in the skin transmitted a true neural image of the sensation in area 1 that was consistently reproduced in the somatosensory cortex.
Understanding the relationship between the discharge of sensory neurons from touch receptors and the perceived intensity of the stimulus is essential for accurately detecting motion activity. The concept of just noticeable difference introduced by Weber 18 and extended by Fechner 19 refers to the smallest difference perceivable between a reference stimulus, such as a palpating finger, and a second stimulus, such as the initial motion induced at a spinal segment.
The amount of motion stimulus necessary to create sensation is the sensation of the just noticeable difference. The sensitivity of a sensory system to differences in sensation is, therefore, a function of the strength of a stimulus. For example, the ability to feel a difference between 1 and 2 kg is easier than feeling a difference between 50 and 51 kg, despite the fact the difference between weights is the same. In accordance with the Fechner—Weber theory, 19 the perception of motion or stiffness at a spinal segment is likely to be more discriminatory when the intensity of the force application is applied in a manner to detect the just first noticeable displacement.
Clinical application of the Fechner—Webner 19 theory to the delivery of PA forces onto spinous processes of a prone patient suggests that the examiner is less able to perceive motion displacement or stiffness when a force of N is applied that results in 2.
A lighter test force, which detects the first noticeable displacement of spinal segmental movement, is likely to be a more accurate motion sensor than stronger test forces that produce more movement. Recognition of the neurophysiological significance for using lighter test forces coupled with the understanding that manual therapists often underestimate the amount of force generated in testing for spinal motion 22 is an important concept for manual therapy instructors.
Most studies examining the encoding of information from peripheral tactile sensory systems have focused on the firing rates of individual neurons which are calculated by spike counts in a given period of time. Tactile perception is influenced by many factors such as aging, finger tip conformation, usage or immobilization, vision, attention, and frequency usage.
The ability of the finger tip skin to conform to the spatial details of a surface or object is also a factor in tactile spatial acuity. Subjects with the most compliant skin on the finger tips produced large indentation compliance with light force and were found to have substantially lower tactile perception thresholds. Therefore, the manner in which the local skin tissue is distorted determines the accuracy of tactile spatial acuity rather than the intensity of pressure delivered.
Since skin conformance was found to be virtually identical in young and old subjects, the loss of spatial acuity with aging is most likely due to changes in the neural mechanisms. Tactile perception is reportedly improved by visual stimulus. Study participants had faster tactile reaction times, 37 improved two point discrimination, 38 and better grating discrimination thresholds ability to discern alternate grooves and ridges with the fingertips while viewing the hand.
The importance of the visual cortex in tactile perception has been further demonstrated by increased activation of the visual cortex near the parieto-occipital fissure on positron emission tomography during tactile discrimination of ridges and grooves that were either wide apart or narrow grating orientation. This is an example of a cross-modal interaction that characterizes normal perception whereby visual imagery is used to enhance tactile sensing.
The attention an examiner devotes to spinal motion palpation may also determine the outcome interpretation. Manipulating the attentive state has been shown to modify the processing of sensory information and alter the perception of vibrotactile stimuli and texture changes. Although the perception of coarse textures, such as embossed dots on a page or the array of teeth on a comb, can be discriminated by spatial cues size, shape, density, and arrangement of the structure , 50 the perception of fine texture is difficult using spatial cues alone.
Eliminating movement interferes with the perception of fine surfaces because, without movement, there is little cutaneous vibration. The Pacinian channels play a more important role than the RA Meissner and Merkel mechanoreceptors channels in discriminating fine textured surfaces. Both channels demonstrate greater discrimination with low-frequency vibrations 10 and 30 Hz than with higher frequency vibrations and Hz. The speed at which a fine textured surface moves over the skin of the finger tip, therefore, affects the ability to discriminate a sensory stimulus.
This study suggests that a slow induction of spinal movement during SMP testing may enhance tactile discrimination. Psychophysiological studies have demonstrated that tactile spatial resolution is greater in blind subjects than in age-matched sighted subjects. Sighted individuals handle and touch the same objects as blind people, but, in contrast to the blind, are not required to focus all of their attention on the geometry and texture of the objects being discriminated.
Further support for the contention that increased use, reliance, and focus improve tactile perception has been demonstrated in a study that immobilized hands and arms of 31 subjects for an average of 5. Discrimination thresholds of the immobilized hand returned to control levels on the non-immobilized side in 2—3 weeks.
Immobilization also appears to have an effect on cortical activation. In contrast to the enlargement of cortical maps from increased use, 2 weeks of immobilization of the index finger resulted in a significant decrease in blood oxygen levels, as measured by functional MRI, within the related S1 area of the somatosensory cortex.
The reduced vascular activation in the somatosensory cortex secondary to enforced immobilization was parallel to the impairment in tactile perception. Increased frequency of use of the hands may also account for the significantly higher spatial acuity in professional pianists as compared to nonmusicians.
Both the pianist and the practitioner of Tai Chi have intensive practice routines potentially enhancing neuronal efficiency and cortical organization of tactile acuity leading to lower spatial discrimination thresholds. Many variables affect tactile perception: finger tip utilized, intensity of the motion stimulus or degree of manual pressure utilized , speed of the motion induced, visual focus to the tactile task, attentiveness to the motion exam, finger tip conformation to the spatial details of the surface, texture of the surface, age of the examiner, and frequency of use of the finger tips Table 1.
Evidence exists for using either the first or second fingers for spinal motion palpation because of the higher number of mechanoreceptors located in these finger tips. Finger contact that optimizes skin conformation to the body surface is recommended in order to lower thresholds of tactile perception in favor of the amount of finger pressure.
Recognition of the just noticeable difference between the motion stimulus induced by the test and the motion event may also increase tactile perception of the movement. Spinal segmental motion analysis of the first noticeable movement induced by a gentle test movement stimulus places emphasis on the evaluation of the neutral zone behavior in the spinal motion segment.
For example, during passive physiological intervertebral motion testing of lumbar segmental forward bending, the manual therapist palpates the ease in which the spinous processes separate upon the first arrival of motion at the segment instead of concentrating on the degree to which the spinous processes separate.
If examining the initial resistance-free movement described as the neutral zone of the spinal motion segment enhances tactile perception, intertherapist reliability may improve. Examination of spinal segmental motion behavior using the just noticeable difference concept may also contribute to the clinical understanding of spinal segmental instability and provide support for motor control management strategies.
The concept of just noticeable difference may also apply to the central PA test commonly used to assess vertebral motion stiffness at the segmental level. Induction of gentle PA force would less likely influence adjacent vertebral segments and thus be more specific to the test segment, but may also allow for greater sensory discrimination of neutral zone behavior than a stronger force used to assess total amount of displacement.
Perhaps previous studies on spinal motion palpation have placed too much emphasis on segmental range of motion and not enough focus on motion quality such as ease or resistance to movement. Full attention to the motion test has also been found to facilitate tactile detection and awareness. Since motion awareness and perception accuracy is enhanced through repetition, the manual therapist is encouraged to use SMP as a routine part of every spinal pain patient examination.
With respect to passive intervertebral motion testing, the examiner should also consider inducing the segmental motion slowly, since the ability to discriminate the sensory motion stimulus is enhanced at slower speeds. Researchers examining reliability of spinal motion examination techniques used by manual therapists need to account for the variables that affect tactile perception in the design of studies assessing spinal segmental movement.
Additional consideration of the variables that affect tactile perception is necessary to obtain meaningful information from SMP tests that help decide an appropriate intervention. The decision to utilize manipulation for the purpose of improving spinal mobility, or a motor control exercise approach to provide spinal stabilization, may be determined at least in part from an accurate interpretation of spinal motion by palpation.
The accuracy in interpreting spinal segmental motion by palpation is, therefore, likely to affect treatment outcome. National Center for Biotechnology Information , U. J Man Manip Ther. Author information Copyright and License information Disclaimer.
Email: moc. This article has been cited by other articles in PMC. Abstract Spinal motion palpation SMP is a standard component of a manual therapy examination despite questionable reliability. Keywords: Spinal motion palpation, Tactile sensibility, Neurophysiology, Reliability. Introduction Spinal motion palpation SMP is used by manual therapists to guide treatment interventions, yet reliable and valid testing methods have not been established. Tactile Sensibility of the Human Hand Understanding the tactile acuity of the hand and fingertips relative to spinal motion testing requires review of the different mechanoreceptors and end organs responsible for mediating the sense of touch.
Open in a separate window. Figure 1. Central Processing of Sensory Motion Stimuli The detection of a movement stimulus is a primary function of higher cortical neuronal activity within areas 1, 2, and 3 of the somatosensory cortex. Age Factor in Affecting Tactile Perception Tactile perception is influenced by many factors such as aging, finger tip conformation, usage or immobilization, vision, attention, and frequency usage.
Skin Conformation and Tactile Acuity The ability of the finger tip skin to conform to the spatial details of a surface or object is also a factor in tactile spatial acuity. Visual Tactile Enhancement of Tactile Perception Tactile perception is reportedly improved by visual stimulus. Attentive State and Sensory Processing The attention an examiner devotes to spinal motion palpation may also determine the outcome interpretation. Sensory Perception Enhancement through Movement Stimulus Although the perception of coarse textures, such as embossed dots on a page or the array of teeth on a comb, can be discriminated by spatial cues size, shape, density, and arrangement of the structure , 50 the perception of fine texture is difficult using spatial cues alone.
Significance of Frequency of Use on Tactile Perception Psychophysiological studies have demonstrated that tactile spatial resolution is greater in blind subjects than in age-matched sighted subjects. Summary Many variables affect tactile perception: finger tip utilized, intensity of the motion stimulus or degree of manual pressure utilized , speed of the motion induced, visual focus to the tactile task, attentiveness to the motion exam, finger tip conformation to the spatial details of the surface, texture of the surface, age of the examiner, and frequency of use of the finger tips Table 1.
Table 1 SMP clinical considerations to improve accuracy and reliability. Variables affecting tactile perception Possible ramifications for SMP Finger tip palpation versus palmar palpation Utilize one of the first two finger tips to assess passive intervertebral motion versus palmer pressure to analyze vertebral spring Trust of the somatosensory impression of the movement stimulus analyzed by palpation Excessive over-analysis of a movement stimulus assessed by palpation may lead to false interpretation of the motion event.
SMP is centrally processed in the somatosensory cortex not the pre-frontal cortex Use of touch sensors or pressure sensors Touch sensors conduct a truer signal of the motion event to the somatosensory cortex than pressure sensors Palpatory contact or force used Use of light contact or force is more accurate than greater force for motion palpation Analysis of the motion event Focus on palpating the initial motion elicited instead of concentrating solely on the amount of motion Age Degradation of tactile receptors with age may affect SMP discrimination.
Take care of your hands and fingers Finger tip skin conformation to the spatial details of the body surface being palpated Skin conformation of the hand and finger tip to the body part palpated enhances tactile perception more than the amount of pressure Actual viewing of the body Actual viewing of the body facilitates the processing of tactile stimuli by presetting neural circuits in the somatosensory cortex Visual imagery Visual imagery enhances tactile sensory discrimination Attentiveness to the motion task Attentional direction to SMP may significantly influences tactile detection and discrimination Test movement induction Slow test movement induction enhances tactile perception of fine textured surfaces i.
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Spinal palpation for lumbar segmental mobility and pain provocation: an interexaminer reliability study. J Manipulative Physiol Ther. Reliability of spinal palpation for diagnosis of back and neck pain: a systematic review of the literature. Huijbregts P. Spinal motion palpation: a review of reliability studies. An investigation of the reliability and validity of posteroanterior spinal stiffness judgments made using a reference-based protocol.
Intertester reliability and validity of motion assessments during lumbar spine accessory motion testing. A treatment-based classification approach to low back syndrome: identifying and staging patients for conservative treatment. A clinical prediction rule for classifying patients with low back pain who demonstrate short-term improvement with spinal manipulation.
Interrater reliability of clinical examination measures for identification of lumbar segmental instability. Arch Phys Med Rehabil. Modality coding in the somatic sensory system. Principles of neural science. Knipestol M, Vallbo AB. Single unit analysis of mechanoreceptor activity from the human glabrous skin.
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Abstract Objective: Segmental passive motion palpation is a common method to detect restrictions in the spine and frequently serves as a basis for decisions concerning further treatment. The purpose of this study was to test the interrater reliability of the specific segmental physiological motion palpation of the lumbar spine in sitting position. Methods: Two raters examined the lumbar spine of 22 participants. Some of the participants were symptomatic and some were asymptomatic.
The spinous processes of L1 to S1 were marked before the examination. The tests were performed in sitting position; the most hypomobile segment was identified for each direction of movement.
The participants were unknown to the raters. Two assistants blinded the raters to the symptoms of the participants and documented the findings.
The interrater reliability was calculated by using Cohen's kappa for two raters, for the three planes, and for each of the directions of movement.
Results: The interrater reliability for motion palpation of the lumbar spine was poor, lying within the range of chance agreement.
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