Amazing stuff! Good news! Makes sense! 😊
"After nine months in the womb, humans enter a world filled with texture and shape. We must then quickly learn to recognize and respond to textures and objects in the outside world, beginning with sensations like the soft feel of a t-shirt or the doughy squish of a sandwich. By learning what touch sensations are innocuous, the brain can better recognize painful insults that might cause damage—think skinning a knee or stubbing a toe. But 7 to 10 percent of the global population develops mechanical allodynia, a form of chronic pain where innocuous light touch is perceived as painful. ...
neuroscientists have discovered that altered neuronal activity in a brain area called the dorsal column nuclei drives mechanical allodynia. The dorsal column nuclei process and categorize light touch information before sending it on to cortical areas that discriminate between different types of touch. In monitoring the activity of mouse neurons in the gracile nucleus, they discovered that mechanical allodynia causes the gracile nucleus’ normal neural activity patterns to become uncoordinated. ...
The dorsal column nuclei’s representation of touch gets transmitted to another area called the thalamus, which also plays a prominent role in pain perception. However, this is mediated by different thalamic regions that receive noxious pain information from specialized pain receptors termed nociceptors.
Normally, these two pathways remain separated, but in the
case of mechanical allodynia, it seems that their wires get crossed at the level of the thalamus and above, in the cortex. Understanding how these wires get crossed is the next step in determining how the brain distinguishes innocuous from painful touch. ...
“By looking at both inflammation-induced and injury-induced mechanical allodynia, we were able to search for common signatures in the patterns of neural activity that characterize this form of chronic pain,” ... “This led us to observe changes in neural processing that point to the dorsal column nuclei as crucial in discriminating innocuous touch from potentially harmful touch.” ..."
From the highlights and summary:
"Highlights
• The DCN is a critical node for mechanical allodynia but not thermal allodynia
• Mechanical allodynia disrupts neural population activity and neural correlations in the GrN
• Altered GrN neural correlations predict increased information transmission to the VPL
• GrNSst VPL projection neurons are required for the expression of mechanical allodynia
Summary
The neural circuits that transmit the sense of pain and how pain is encoded by these circuits are still poorly understood.
Mechanical allodynia is a prominent form of chronic pain characterized by painful responses to innocuous touch that develops as a consequence of nerve damage and inflammation.
Here, we show that alterations to the normal log-normal distribution of neuronal activity and structure of neural correlations between neurons in the dorsal column nuclei (DCN) constitute a signature feature of mechanical allodynia, with the transmission of “allodynic” light touch information to the thalamus by somatostatin-positive projection neurons in the DCN being essential for its expression and development.
Our findings are consistent with neural activity in the DCN encoding a reference landscape of tactile percepts that animals use to differentiate innocuous touch from potentially noxious mechanical stimuli."
The dorsal column nuclei encode and transmit the network signatures of mechanical allodynia (open access)
Graphical abstract
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