LSD selectively alters the functional connectivity between specific thalamic nuclei and sensory and associative cortical areas. Using structural and resting-state functional MRI in healthy volunteers under acute LSD administration, researchers found increased coupling of the ventral complex, pulvinar, and non-specific thalamic nuclei with somatosensory and auditory cortices, as well as with associative cortex regions rich in serotonin 2A receptors. At subcortical levels, LSD increased connectivity among these thalamic nuclei but decreased striatal-thalamic connectivity. These nucleus-specific changes help explain LSD's modulation of subcortical-cortical circuits and associated behavioral effects.
LSD alters brain functional connectivity and local signal amplitude in opposite directions depending on the type of serotonin receptor involved. In healthy volunteers, LSD increased activity and connectivity in cortical regions of the default mode and attention networks, which have high densities of 5-HT2A receptors; these changes correlated with visual hallucinations. Conversely, LSD decreased activity and connectivity in limbic areas rich in 5-HT1A receptors. The spatial patterns of these functional changes overlapped with the distribution of the two serotonin receptor subtypes, suggesting distinct receptor-mediated mechanisms underlie LSD's reorganization of brain networks.
Meditation can be divided into focused attention (FA) and open monitoring (OM) styles, which involve different attentional and awareness processes. In a functional magnetic resonance imaging study, Theravada Buddhist monks expert in both FA and OM meditation, along with novices with 10 days of practice, were scanned. Expert meditators showed massive self-regulation of fronto-parietal and insular areas in the left hemisphere, depending on the meditation state. Anterior cingulate and dorsolateral prefrontal cortices played opposing roles in executive control of attention. The findings resolve a controversy about whether meditation involves hypo- or hyperfrontality, and suggest that mental practice reorganizes brain activity patterns, especially in prefrontal cortex and insula.