Developments in autonomic research: a review of the latest literature

Abstract

Small-diameter afferents do not just subserve pain and temperature sensibilities, important for protection of the body though they are: there is a system of lowthreshold unmyelinated afferents that respond to light stroking (C-tactile afferents) and they are believed to subserve the affective components of touch. Patients with large-fibre sensory neuropathies exhibit skin sympathetic responses to stroking, and report the stimuli as feeling pleasant. Moreover, the posterior insula is activated. Patients with small-diameter sensory neuropathies, specifically those with congenital insensitivity to pain, suffer from cumulative injuries that can lead to joint degeneration. There is evidence that the nociceptive (and sympathetic) axons die because nerve growth factor is not being produced by the target tissues; patients with congenital insensitivity to pain have mutations in the NTRK1 gene, the gene responsible for producing the TrkA receptor, but there is also evidence for mutations in the SCN9A gene, which codes for a specific subunit of the voltage-gated sodium channel. Specific mutations, leading to clusters of cases of congenital insensitivity to pain, have been found in several geographical locations, with several genetic mutations having been documented. Interestingly, even patients with congenital insensitivity to pain, despite having never experienced pain, can still empathise with the pain in others-we do not need to feel pain in order to empathise, but we do need to feel pain in order to ensure that our body looks after itself.

The Effect of Low-Frequency Physiological Correction on the Reproducibility and Specificity of Resting-State fMRI Metrics: Functional Connectivity, ALFF, and ReHo

“…Similar interactions may apply to CRV and RVT, as suggested by a number of previous studies (Shea, 1996; Birn et al, 2009; Macefield, 2009). While these studies and our own have recommended the removal of global physiological signals to improve the reliability of rs-fMRI measures, the relationship between these signals and rs-fMRI signal is still actively investigated.…”

Frequency-specific network topologies in the resting human brain

“…However, although using this method for physiological correction can suppress over-estimation of functional connectivity, it might cause under-estimation because variations in physiological regulations might be correlated with neural activities (Murphy et al, 2013 ). For example, emotional arousal and activity levels of the autonomic nervous system are indicated by variability of heart rate (Macefield, 2009 ). Furthermore, it is unclear whether there are regional specific physiological confounds.…”

Resting-state fMRI confounds and cleanup

“…Variations in cardiac rate, respiration, arterial CO 2 concentration or blood pressure may be correlated with the variations in neural activity that we would like the BOLD signal to capture. For example, heart rate variability is an indicator of emotional arousal and autonomic nervous system activity (Macefield, 2009) and breathing variations are often tied to emotional state (Shea, 1996). If neural activity in the resting-state network under investigation is linked to, or synchronous with, any of these physiological processes, removing the physiological confound will also remove these neural activity-related BOLD fluctuations.…”