Squirrel monkey lateral thalamus. II. Viscerosomatic convergent representation of urinary bladder, colon, and esophagus

Abstract

The response properties of 106 visceroceptive lateral thalamic neurons were investigated in anesthetized squirrel monkeys. Most neurons were located in the ventral posterior lateral nucleus (VPL), and a smaller number of cells was also found in a variety of thalamic nuclei around VPL. Ninety (85%) of these cells responded to distension of the urinary bladder, the distal colon, and/or the lower esophagus. The majority of the visceral-responsive cells also had convergent somatic and multivisceral responses (71% of the 85%). A small population (6%) was visceral specific; that is, these neurons were not activated with somatic stimuli. Visceral responses were excitatory, inhibitory, or mixed, and most were either visceral nociceptive specific (65%) or visceral wide-dynamic-range type (34%). Very few visceral responses (1%) could be classified as low threshold. The incidence of these response types were highly dependent on the specific viscus stimulated. Most visceral responses were able to code stimulus duration and intensity. The majority (69%) of the visceroceptive neurons had somatic low-threshold convergent input mainly from the surface of the lower body. The somatic receptive field locations and the somatic response properties seem unrelated to the convergent visceral input and the visceral response properties, although there were some exceptions. No obvious viscerotopical organization was found in VPL. The results lead us to propose two different modes of representation for processing of and distinguishing between visceral and somatic inputs: a distributed population code for visceral inputs, and a local code for somatic inputs. Based on these codes, we discuss a new hypothesis for referred pain.

Brain white matter changes associated with urological chronic pelvic pain syndrome: multisite neuroimaging from a MAPP case–control study

“…Similarly, the spinal cord contains no known neurons that solely convey visceral input, given the spinal convergence of overlapping visceral and somatic afferent nerve fibers [8]. On the other hand, the primary supraspinal region that initially receives nociceptive input, the ventral posterolateral nucleus of the thalamus, distinguishes abdominal from pelvic visceral input, although it lacks visceral topography from pelvic viscera [7]. If regional patterns of brain activity are insufficient to distinguish types of visceral pain, as these studies suggest, it is feasible that cortical representations of visceral pain are mediated by other features of neural information processing, such as the microstructure of axonal tracts that communicate pain-related information.…”

Neural control of the lower urinary tract: Peripheral and spinal mechanisms

“…There is extensive convergence of pelvic organ input107,108 at the levels of the spinal cord, dorsal column nuclei, solitary nucleus, medullary reticular formation, and thalamus 109. Convergent processing underpins the coherent functioning of systems controlled by efferent outflows diverging from a common starting point, as exemplified by the synergic coordination of bladder and urethra required for normal voiding.…”

Pain and functional imaging

“…Indeed methods other than functional neuroimaging have provided the basic information on the supraspinal organization of the pain systems. Advanced anatomical electrophysiological methods have revealed numerous ascending tracts and nociresponsive supraspinal structures BrÏggemann et al 1994;Craig et al 1994;Guilbaud et al 1994). Functional neuroimaging allows the recording of functional activity across the whole brain simultaneously and with equal sensitivity.…”