Key result
Noxious thermal stimulation to the foot compared to the hand delayed primary sensory network activation by 3.6 +/- 1.3 s, with no significant delay (0.6 +/- 2.1 s) in reward/aversion circuitry.
Why the study?
Does the site of noxious thermal stimulation (foot vs hand) affect the delay of hemodynamic responses in primary sensory and emotion circuitry?
Does the site of noxious thermal stimulation (foot vs hand) affect the delay of hemodynamic responses in primary sensory and emotion circuitry?
Answers are grounded in this paper and cite their sources.
The rapid onset of reward/aversion circuitry activation regardless of stimulation site suggests a fast protective mechanism for survival, independent of the conduction distance delays seen in primary sensory networks.
Recently, functional magnetic resonance imaging has been used as a novel method of evaluating the CNS response to noxious stimuli. In a previous study, a prolonged noxious thermal stimulus applied to the dorsum of the hand produced more than one hemodynamic response that was temporally segregated. The two major responses displayed activation in primary sensory regions (classic pain circuitry) and regions involved in emotion (reward/aversion circuitry), respectively. In the current study, we applied the same thermal stimulus separately to the dorsum of the left foot and the dorsum of the left hand in the same subjects and compared the hemodynamic responses to evaluate the effects of conduction distance on CNS activation within these two segregated systems. After stimulus delivery to the foot, the hemodynamic response in primary sensory networks occurs after a delay of 3.6 +/- 1.3 s as compared with the response after hand stimulation. The relative delay of the hemodynamic response in reward/aversion regions is not significantly different between hand and foot stimulation (0.6 +/- 2.1 s). These results within the primary sensory system are consistent with the greater conduction distance of the peripheral nerves from the hand versus the foot. The observation that the response within the reward/aversion pathways occurs with the same rapid temporal characteristics after either hand or foot stimulation supports the notion that the circuitry involved in the evaluation of aversive stimuli is rapid in onset and probably represents a major protective mechanism for survival.
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Becerra et al. (2004) studied this question. Noxious thermal stimulus to the foot vs. Noxious thermal stimulus to the hand was evaluated on Hemodynamic response delay in primary sensory networks and reward/aversion regions. Noxious thermal stimulation to the foot compared to the hand delayed primary sensory network activation by 3.6 +/- 1.3 s, with no significant delay (0.6 +/- 2.1 s) in reward/aversion circuitry.
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