Phantom limb experience after brachial plexus anaesthesia.

There are more than two million amputees in the USA, and almost all will experience phantom limb sensations (PLS), describing the missing limb as still present. They may also experience intense pain, known as phantom limb pain (PLP), a considerable factor in poor quality of life. In some upper extremity amputees and following brachial plexus avulsion injury (BPAI), hand digits can be detected and mapped to distinct facial skin areas, termed hand-to-face remapping.

Sources of Rapid and Delayed New Lower Jaw Input in the Forepaw Barrel Subfield (FBS) in Rat Primary Somatosensory Cortex (SI) Following Forelimb Deafferentation.

Previously, we reported an immediate emergence of new lower jaw input to the anterior forepaw barrel subfield (FBS) in primary somatosensory cortex (SI) following forelimb deafferentation. However, a delay of 7 weeks or more post-amputation results in the presence of this new input to both anterior and posterior FBS. The immediate change suggests pre-existing latent lower jaw input in the FBS, whereas the delayed alteration implies the involvement of alternative sources.

Lower jaw-to-forepaw rapid and delayed reorganization in the rat forepaw barrel subfield in primary somatosensory cortex.

We used the forepaw barrel subfield (FBS), that normally receives input from the forepaw skin surface, in rat primary somatosensory cortex as a model system to study rapid and delayed lower jaw-to-forepaw cortical reorganization. Single and multi-unit recording from FBS neurons was used to examine the FBS for the presence of "new" lower jaw input following deafferentations that include forelimb amputation, brachial plexus nerve cut, and brachial plexus anesthesia. The major findings are as follows: (1) immediately following forelimb deafferentations, new input from the lower jaw becomes expressed in the anterior FBS; (2) 7-27 weeks after forelimb amputation, new input from the lower jaw is expressed in both anterior and posterior FBS; (3) evoked response latencies recorded in the deafferented FBS following electrical stimulation of the lower jaw skin surface are significantly longer in both rapid and delayed deafferents compared to control latencies for input from the forepaw to reach the FBS or for input from lower jaw to reach the LJBSF; (4) the longer latencies suggest that an additional relay site is imposed along the somatosensory pathway for lower jaw input to access the deafferented FBS.

Structural and functional organization of the lower jaw barrel subfield in rat primary somatosensory cortex.

Barrel subfields in rodent primary somatosensory cortex (SI) are important model systems for studying cortical organization and reorganization. During cortical reorganization that follows limb deafferentation, neurons in deafferented forelimb SI become responsive to previously unexpressed inputs from the lower jaw. Although the lower jaw barrel subfield (LJBSF) is a likely source of the input, this subfield has received little attention.