Receptive fields

[Diane]

I'm finding out that receptive fields means different parts of the nervous system depending on what you want to examine. The whole thing is a "receptive field", really..

Anyway, here is a link to a neuroscience edition on pubmed, found by searching, receptive fields (http://www.ncbi.nlm.nih.gov/sites/entrez?db=books&doptcmdl=DocSum&term=receptive+fields+AND+neurosci%5Bbook%5D).

Here is a juicy tidbit: Until recently, the temporal structure of such stimuli was not considered a major variable in characterizing the physiological properties of somatic sensory neurons. For instance, the classical definition of the receptive field of a somatic sensory neuron takes into account only the overall area of the body surface that elicits significant variation in the neuron's firing rate (see text). By the same token, the topographic maps in the somatic sensory system have been interpreted as evidence that tactile information processing involves primarily spatial criteria.

The advent of multiple electrode recording to simultaneously monitor the activity of large populations of single neurons has begun to change this “static” view of the somatic sensory system. In both primates and rodents, this approach has shown that the receptive fields of cortical and subcortical neurons vary as a function of time: The neuron responds differently to a spatially defined stimulus as the period of stimulation proceeds (see figure).

In other words, a slow light stimulus might just lessen the overall work load of doing manual therapy. :)

[Barrett Dorko]

So, this is evidence that the patient's report of a spreading and geographically changing sensation (over time) in response to a touching of a single spot on the skin makes sense - given what the study indicates?

[Diane]

Barrett, it's not a single study. Here's the link (http://www.ncbi.nlm.nih.gov/books/bv.fcgi?highlight=receptive,fields&rid=neurosci.box.626) where I took the excerpt. It's more a compilation/reflection of several studies (listed at the bottom of the page).

[Diane]

Here is an open access article (http://www.behavioralandbrainfunctions.com/content/1/1/18) examining the topic (cutaneous). Figure 6 is worth clicking on to get the big version.

[Diane]

Here are a few examples of receptive fields of skin (http://www.somasimple.com/forums/showthread.php?p=43815#post43815).

[Diane]

When considering receptive fields, we have to see an afferent peripheral neuron as a two-armed entity. It has one long arm out to the surface of the body (skin), or other bits inside (less long but smaller in diameter or less myelinated). Its other arm goes into the dorsal horn, where it offers its info to the CNS. It has a receptive field on the end of one of its "arms", and at the other end, the info is funneled up and processed along the way, ending up in a totally enclosed second or even third or fourth, "receptive" field, where it is finally perceived by the "captain" of the "ship", the S.S. Humanantigravitybodysuit.

Look here (http://www.somasimple.com/forums/showpost.php?p=43844&postcount=2) for a little excerpt I made on receptive fields.

When we manually explore objects, multiple contacts between the skin and the object surface generate extraordinarily complex patterns of tactile stimuli. OK...
As a consequence, the somatic sensory system must process subtle signals that change continuously in time. OK... Nonetheless, we routinely discriminate the size, texture and shape of objects with great accuracy. OK...
Until recently, the temporal structure of such stimuli was not considered a major variable in characterizing the physiological properties of somatic sensory neurons. For instance, the classical definition of the receptive field of a somatic sensory neuron takes into account only the overall area of the body surface that elicits significant variation in the neuron's firing rate (see text). By the same token, the topographic maps in the somatic sensory system have been interpreted as evidence that tactile information processing involves primarily spatial criteria. Limitations of methodology..

The advent of multiple electrode recording to simultaneously monitor the activity of large populations of single neurons has begun to change this “static” view of the somatic sensory system. Hurray! :clap2:
In both primates and rodents, this approach has shown that the receptive fields of cortical and subcortical neurons vary as a function of time: The neuron responds differently to a spatially defined stimulus as the period of stimulation proceeds. Wow, the brain can change it's reception of incoming over time. And it can be shown and mapped. This is good.
This coupling of space and time can also be demonstrated at level of somatotopic maps (see text). By recording the activity of single neurons located in different regions of the map simultaneously, it is apparent that the stimulation of a small area of the skin tends to excite more and more neurons as time goes by. I had a feeling it could, but it's nice to see people can prove it.
Thus, many more neurons than those located in the area of the map directly representing the stimulated skin actually respond to the stimulus, albeit at longer latencies. OK...
The end result of these more complex neuronal responses is the emergence of spatiotemporal representations at all levels of the somatic sensory system. Thus, contrary to the classical notion of receptive fields, the somatic sensory system processes information in a dynamic way. Such processing is not only relevant for the normal operation of the system, but may also account for some aspects of adult plasticity. Hurray! :clap2: