No abstract

No abstract

Studies utilizing the expression of Fos protein as a marker of neuronal activation have revealed that pain of deep somatic or visceral origin selectively activates the ventrolateral periaqueductal gray (vlPAG). Previous anatomical tracing studies revealed that spinal afferents to the vlPAG arose from the superficial and deep dorsal horn and nucleus of the dorsolateral funiculus at all spinal segmental levels, with approximately 50% of vlPAG-projecting spinal neurons found within the upper cervical spinal cord. This study utilized detection of Fos protein to determine the specific populations of vlPAG-projecting spinal neurons activated by noxious deep somatic or noxious visceral stimulation. Pain of cardiac or peritoneal (i.e., visceral) origin activated neurons in the superficial and deep dorsal horn and nucleus of the dorsolateral funiculus of the thoracic cord, whereas pain of hindlimb (i.e., deep somatic) origin activated neurons in the same laminar regions but in the lumbosacral cord. Each of these deep noxious manipulations also activated neurons in the superficial and deep dorsal horn and nucleus of the dorsolateral funiculus of the upper cervical spinal cord. In a second set of experiments, the combination of retrograde tracing and Fos immunohistochemistry revealed that vlPAG-projecting spinal neurons activated by deep somatic pain were located in both the upper cervical and lumbosacral cord, whereas those activated by visceral pain were restricted to the thoracic spinal cord. Thus pain arising from visceral versus deep somatic body regions influences neural activity within the vlPAG via distinct spinal pathways. The findings also highlight the potential significance of the upper cervical cord in integrating pain arising from deep structures throughout the body.

Functional magnetic resonance imaging was performed in 16 healthy subjects while they undertook orientation discrimination tasks of real rotating and mentally rotating alphanumeric characters. Perception of rotating and stationary abstract characters was also performed. Mental rotation and the perception of alphanumeric characters undergoing real rotation activated equivalent cortical areas, in keeping with the analogue hypothesis of mental rotation. In addition, areas along the dorsal stream, including the V5/middle temporal complex and the intraparietal sulcus (IPS), were activated during both the real and imaginary rotary conditions. Within the parietal lobe there were areas of convergence (i.e., recruited by all three motion conditions) and areas of divergence (i.e., selectively activated by a particular condition). Tasks requiring canonical-mirror orientation discrimination revealed involvement of neural substrates localized to the ventrolateral bank of the IPS. Tasks in which this judgment was not performed and during which the subject viewed rotary motion of abstract stimuli recruited activity in the medial bank of the IPS. These results indicate subspecialization of the human posterior parietal lobe according to function.