The Sensory Hand, by Vernon B. Mountcastle

[Diane]

I am sinking luxuriously into this book, The Sensory Hand (http://books.google.ca/books?id=WOmqKSheygYC&dq=the+sensory+hand+mountcastle&pg=PP1&ots=eA_i_n6w84&sig=n5rgtJEcPf0eY0x8LnLYkaRRgAc&hl=en&prev=http://www.google.ca/search?hl=en&q=The+sensory+hand+Mountcastle&btnG=Google+Search&sa=X&oi=print&ct=title&cad=one-book-with-thumbnail)(2005), by Vernon Mountcastle.

Here is a thorough review (http://brain.oxfordjournals.org/cgi/content/full/129/12/3413) of this book by Edward Jones. In it you will find one of the most complete descriptions I've ever read of the innervation of the hand (I haven't got very far into the book itself yet).

I think I have put Vernon B. Mountcastle into the Pharaohs section (or if I haven't already I will), because he has tackled the sensory motor system of the body, the one that primarily concerns manual therapists. He writes about what he terms a somesthetic experience, and really got my attention when he mentioned the insula.

This is from the forward:
"A general hypothesis I consider at several places in this book is that the small-fibered afferent systems, long known to contain the essential neural substrates for pain and temperature sensibilities, also contribute to the higher-order aspects of the several varieties of mechanosensitive sensibility. They are activated under many conditions by the same mechanical stimuli processed in the large-fibered system, and carry signals to the forebrain that evoke the overall affective components of the sensory experiences. These small-fibered afferent systems activate many distributed areas in the frontal lobe, the limbic areas of the cerebral cortex, and the insula.

At the same time signals in large-fibered afferents are processed in an elegant and quantitative manner and present to higher-order cortical systems signals that can be detected, discriminated and rated with precision, in quantitative correspondence with the parameters of the stimuli that evoke them. Until now we have learned very little about the final "integration" of these varied inputs in producing overall somesthetic experiences. This integration and its varieties are obvious in everyday life - the touch of a loved one's hand carries overtones not found in more ordinary tactile experiences.

The hitherto perceived dichotomy of these two classes of systems has resulted in a parallel separation of investigators. Those talented individuals who have made such spectacular discoveries about the functions of the small-fibered systems in pain and temperature sensibilities now sense that the deepening knowledge of these systems, particularly the molecular aspects of the peripheral transducer mechanisms, will lead to chemical methods of blocking pain at its level of inception,with no effects on the function of the central nervous system. Yet, only a few have taken full account of the broader - or perhaps I should say, other - meanings for behavior of activity in the small-fibered systems. Of course, the same is true inversely for those investigators involved in quantitative studies of the brain mechanisms in mechanoreceptive sensibility. They have because of the constraints of experimental design and execution not been able to take into account the accompanying activity in the small-fibered systems and the powerful contributions they make to the overall somesthetic experience. I think this dichotomy also may have contributed to the PT profession's manual therapists having fallen into two halves as well.

This division now ends, and concerted efforts are directed to study of the somatic system, complete. That such a dichotomy has not occurred, or at least not to the same extent, in studies of the visual and auditory systems is attributable to the relative simplicity of those systems. Compare, for example, the 12 different sets of first-order fibers innervating the primate hand with the much smaller number of afferent sets leaving the eye or the ear. The visual and auditory systems are by no means simple, but only appear so when compared with the somatic afferent system, in which a number of afferent sets with congruent peripheral distributions feed many ascending systems. Moreover, at several transition stations of these systems there is a complex interaction with motor mechanisms.

I make here an effort to begin the process of unifying these two major fields of research. The reader will find in several chapters descriptions of the small fiber systems, with some effort to show how they condition the overall mechanoreceptive sensory experiences." I have a feeling this researcher and this book will be a good resource for the Third Way (http://barrettdorko.com/articles/third_way.htm).

Additional links:
1. Wikipedia entry on Vernon Mountcastle (http://en.wikipedia.org/wiki/Vernon_Mountcastle)
2. A A biography (https://sciencegrants.dest.gov.au/SciencePrize/Pages/Doc.aspx?name=previous_winners/Aust1993Mountcastle.htm)
3. The Brain Voyager: Catching up with "the Jacques Cousteau of the Cortex" (http://www.hopkinsmedicine.org/hmn/W07/classnotes.cfm)

[Diane]

The General Properties of Somesthesis (p. 9)

Primary and Complex Varieties of Somesthesis


The equivalent terms somesthesis and somatic sensibility include several varieties of perceptual experiences evoked by stimulation of the tissues of the body. These subjective experiences vary greatly, especially in the emotional overtones that sometimes accompany them.
Mechanoreceptive perceptual experiences are evoked by stimulation of the skin, muscles, joint capsules, and ligaments. Pain, warmth, coolness are evoked by qualitatively different modes of stimulation, and are readily identified as unique by human observers.
The peripheral afferent fibers serving cutaneous pain and temperature perception are interdigitated with those serving mechanoreceptive sensibilities, and the afferent pathways for pain and temperature are integral parts of several ascending somatic systems.

The primary features of the mechanical stimuli impinging upon the skin and deep tissues of the hand are selectively transduced at the peripheral ends of primary afferent fibers and by the multicellular receptor organs innervated by some terminals. The terminals and receptors differ greatly in their selective transducer functions and are arranged in overlapping spatial mosaics. The glabrous skin of the hand is a filter for stimulus quality; different sets of fibers respond at lowest threshold to some particular parameters of mechanical stimulation. I shall from place to place consider the importance of pain and temperature, with special reference to how these sensory inputs influence mechanoreceptive sensibility.


Primary: Several components of somatic sensibility are classed as primary, for they can be evoked by afferent input restricted to a single set of first-order afferent fibers.
Complex: While observers identify other mechanoreceptive modes as equally unique, they are thought to be more complex because they are generated by combinations of afferent input in two or more sets of primary fibers.

I call these different qualities of somesthesis modalities, defined here in a restricted sense as the sensory experiences evoked by stimulus parameters that activate selectively a particular set or sets of primary afferent fibres. In this sense the term is in many but not all cases identical with Helmholtz's more general definition of modality as composed of a class of sensations connected along a qualitative continuum. The singularity of some qualities of somesthesis can be demonstrated in the constrained environment of the combined psychophysical-neurophysiological experiment; several examples are given in later chapters. Somesthetic experiences of everyday life are produced by blends of those regarded as primary, evoked by simultaneous activity in several sets of primary afferent fibers. The inferred convergence between neural signals in different sets of specific afferent fibers has not been observed in the major superhighway of the system, its lemniscal component, which is composed of parallel modality-segregated channels that project to and through the primary somatic sensory cortex of the postcentral gyrus. Present evidence implicates that the convergences and integration of several primary qualities to produce more complex ones like stereognosis occur in trans-postcentral areas of the parietal lobe and the Sylvian fissure.

Attributes of Somesthesis

The different features of the mechanical stimuli that impinge upon us or that we ourselves generate by movements and postures are selectively transduced at the terminals of sensory nerve fibers innervating the skin and the deep tissues of the body. This filtering process is accomplished by transducer mechanisms located either in the nerve terminals themselves or in the sensory "organs" in which those nerve terminals terminate, such as the Meissner's corpuscles of the glabrous skin of the primate hand (Malinovsky 1996). Under normal conditions in peripheral tissues, sensory receptors are narrow filters often selectively tuned to special features and to limited quantitative rages of stimulus parameters.

The total input pattern evokes sensory experiences with several general properties or "attributes." The idea that sensations have general attributes is an old one in experimental psychology. Several somesthetic modalities share the same attributes. Prominent among these is local sign, which is associated with spatial extension and duration in time. A stimulus delivered to the hand of a waking human is readily localized to the spot stimulated. Errors in spatial localization vary from a few millimeters for the densely innervated hand and face to several centimeters for the least densely innervated regions, the trunk, and proximal limbs. A local or spatially extended mechanical stimulus to the skin evokes a local or extended zone of increased neural activity propagated through the somatic afferent system to a spatially appropriate location in the map of the body surface in the somatic sensory areas of the postcentral gyrus. How such local or extended zones of incremented neural activity are interpreted in terms of the location and extent of the stimulated site on the body surface is unknown. This relates to the more general problem of the meaning for function of place in the sensory and motor systems of the brain.

The quality of a stimulus is signaled with some certainty, and that quality is the same no matter how a particular set of afferent fibers is excited. The attribute of quality obtains for each of the varieties of somesthesis. This principle of the labeled line derives from Muller's 1838 doctrine of specific nerve energies (see Chapter 4), now combined with the principle of stimulus selectivity of sensory endings. These principles have been confirmed and extended in studies of the peripheral and central components of the somatic afferent system in nonhuman primates. This large body of knowledge has been extended for the first-order fibers by recording from single afferent fibers in the peripheral nerves of waking humans. A question of special interest is the association of particular patterns of activity ("neural codes") with particular labeled lines.

Mechanical stimuli delivered to the body are distributed (prothetic ) and extensive (metathetic ) continua. Contrast, for example, the series of sensations evoked by mechanical stimulations of different forces delivered to the skin (intensive) as opposed to a series of positions of the fingers at their joints (extensive). More complicated stimuli, the most common, may of course possess both intensive and extensive properties. The afferent signals evoked by two stimuli of different amplitudes allow humans to discriminate precisely between them when the two can be compared directly. We perform poorly when asked to rank the intensities of a number of stimuli along a prothetic continuum by subjective magnitude estimation. The capacity of humans to discriminate between somesthetic stimuli was the subject of the original studies of Weber (1834; translated 1978), which led Fechner (1860) to the science of psychophysics. Weber studied the judgments of lifted weights, which is now thought to be a complex matter that depends on both the pressure of the weight on the skin of the hand and on a central judgment of the effort required to lift the weight, called the "sense of effort." The latter is defined as an internal perception of the intensity of the motor commands emitted, and is often incommensurate with the force produced by those commands, for example, during fatigue (Burgess and Jones 1997; Gandevia 2001). In addition to signals of these attributes of place, spatial extent, temporal duration, quality, and intensity of stimuli that impinge on the surface of the skin, the cutaneous mechanoreceptive afferents provide population signals of the form and the surface microstructure of spatially extended stimuli. In brief, population coding means that information about a particular sensory attribute is signaled by the temporal and spatial relationships between the trains of impulses in elements of the active population, and can be derived neither from the pattern in any single neural element nor by any simple summation of the activity in many elements. Mechanoreceptive, cutaneous afferent fibers play important roles in the haptic appreciation of three-dimensional form called stereognosis, in combination with signals in afferent fibers innervating the deep tissues of the hand.

Metathetic: Any stimulus dimension that can vary continuously and in so doing produce discrete or qualitative changes in perception, the standard example being the wavelength or frequency of visible light, which produces qualitatively different hues or colours as it varies continuously, whereas sound produces continuous or quantitative perceptual changes. (From Greek metathetikos able to change, from meta beside + tithenai to place + -ikos of, relating to, or resembling)

Prothetic: prothetic stimulus dimension n. Any stimulus dimension that varies continuously and produces continuous changes in perception, the standard example being the wavelength or frequency of sound, which produces continuous changes in perceived pitch as it varies continuously, whereas light produces qualitative perceptual changes. (From Greek prothetikos placed in front, from pro before + tithenai to place + -ikos of, relating to, or resembling)


Color added for emphasis. I learned some new words yesterday, these ones based on Greek.

[Pernkopf]

Diane,

Are you finding in this book that the descriptions of neurophysiology are useful in understanding the whole central nervous system or is this book about the hand experience only. I ask because I need a good neurophysiology text at this point. It seems very well written from your excerpts. Thank you for posting about it.

Karen

[Diane]

Karen, you can check it out thoroughly, as most of it is online here (http://books.google.ca/books?id=WOmqKSheygYC&dq=the+sensory+hand+mountcastle&pg=PP1&ots=eA_i_n6w84&sig=n5rgtJEcPf0eY0x8LnLYkaRRgAc&hl=en&prev=http://www.google.ca/search?hl=en&q=The+sensory+hand+Mountcastle&btnG=Google+Search&sa=X&oi=print&ct=title&cad=one-book-with-thumbnail). There's even a link to the contents. It's the best one I've ever seen... but I guess it depends on what you're looking for, ... exactly.

[Pernkopf]

Diane,

I was fascinated by posts Barrett had made about Evelyn Glennie and I thought perhaps readers might get reacquainted with her here (http://www.ted.com/talks/view/id/103). My thinking is how her hands/body became her ears and that this book helps explain such a complex process.

My best regards to all the Neuronauts in this forum.

Karen

[Diane]

She sure can play. Wow.

[Diane]

I want to link this thread to this thread (http://www.somasimple.com/forums/showthread.php?t=5635).

Also, here is a link to a post (http://www.somasimple.com/forums/showpost.php?p=53447&postcount=2) that shows the preference in the somatosensory cortex for skin input over deeper tissue input.

I'm learning about cortical columns now, from the two Mountcastle books. Mountcastle discovered the neocortex was configured in this arrangement, about 25-30 years ago.

[Diane]

I looked into Mountcastle's book, Sensory Hand, to find out what there was to know about Ruffinis. These are SA-IIs, i.e., “slow-adapting type II" mechanoreceptive afferents of a wide fibre type, A-beta.

1. Do they innervate the monkey hand? Definitely not. Nothing in the SA-II category is to be found.
2. Do they innervate the human hand? Apparently not - very few if any specific "Ruffinis" are to be found there; however, there are lots of SA-IIs, which Mountcastle refers to as "Ruffini afferents." Maybe there is a difference drawn somewhere between a) Ruffinis and b) Ruffini afferents, but it is not made explicit in this passage.
3. They continuously fire during sustained stretch of skin, but are not directly perceived as sensation in microneurography.

So I will take Mountcastle's word on this as the final word. (P. 127) Ruffini Corpuscles (SA-II)
Ruffini (1905) discovered in the human dermis and deep connective tissue a multicellular receptor organ that resembles the Golgi tendon organ of muscle. It consists of tightly packed collagen fibers oriented between, parallel to, and sometimes encircled by the dividing terminal branches of the afferent myelinated fiber and its accompanying Schwann cells (Chambers et al. 1972). The capsule of the Ruffini ending is incomplete in many locations, and the details of Ruffini structure vary from place to place. Ruffini corpuscles are found in the subcutaneous connective tissue of the hairy skin of many mammals and in some skin regions within the hair follicles themselves (the “pilo-Ruffini complex,” Biemesderfer et al 1978; Munger 1982; Halata 1988), and in the connective tissue surrounding joint capsules and tendon sheaths. Myelinated afferent fibers putatively linked to Ruffini receptors in the hairy skin of mammals and the glabrous skin of humans are classed as SA-IIs. They possess two defining properties: they are sensitive to stretch of the skin, sometimes with orientation preferences, and they discharge regular trains of impulses for long periods of time in response to sustained mechanical stimulation of the skin (Johansson and Vallbo 1979; Torebjork et al 1987). Published descriptions of more than 1300 large mechanoreceptive afferents innervating the glabrous skin of the human hand show that 18-20 percent were classified by these properties as SA-IIs. A similar survey of published descriptions of large mechanoreceptive afferents innervating the glabrous skin of the monkey hand revealed that only 5 of more than 15000 were classified as “SA-IIs” My colleagues and I have studied several thousand slowly adapting afferents innervating the glabrous skin of the monkey hand, with controlled conditions of stimulation and quantitative analyses of the impulse discharge patterns in the responses evoked by steadily maintained mechanical stimuli. The fibers studied were beyond any reasonable doubt Merkel slowly adapting afferents, activated from small receptive fields on the dermal ridges of the glabrous skin: only a few were classified as sensitive to skin stretch. Skin stretch sensitivity does occur in some fibers of the SA-I population (Bisley et al., 2000), and a regularity of discharge is almost universal during the “early steady state,” the first half-second of the response (Mountcastle et al 1966). This population cannot be divided on the basis of the SA-I/SA-II differences that separate so clearly the two populations innervating the glabrous skin of the human hand.

It appears that Ruffini afferents are present in the hairy skin of the human hand and not in the glabrous skin of either human or monkey hands, but axons with SA-II properties have been identified in the innervation of the glabrous skin of the human hand. No other difference between the innervations of the human and monkey hands has been discovered. There is some uncertainty about the role of these afferents in signalling the shape of objects grasped by the hand, now attributed in humans to Ruffini afferents, for this manual skill is well developed in monkeys and critical for survival in their lives in the trees. A serial section study of an entire monkey hand uncovered not a single clearly identifiable Ruffini corpuscle, and only one was found in human finger glabrous skin (Pare et al. 2003).

Stimulation of single SA-II afferents innervating the glabrous skin of the human hand, recorded via microneurography in waking humans, evokes “no distinct and constant quality of sensation” (Torebjork et al. 1987), an observation confirmed in several laboratories (Ochoa and Torebjork 1983; Schady et al. 1983; Vallbo et al 1984; Macefield et al 1990).

Whatever the ultimate story on Ruffinis in the palm of the hand turns out to be, they are well and densely sprinkled throughout the skin everywhere else, and in all mammals. When we treat patients, we are likely to be affecting them directly in our patients for as long as we hold manual contact; when we use our hands, we are registering our own contact through lots of afferents in there, many of which are capable of coding continuous stretch and are SA-IIs, even if they aren't Ruffinis by some peoples' definitions.