Smokers are at risk of developing a range of serious illnesses, including cancers of the throat, lungs and pancreas, heart disease and respiratory diseases. They also suffer from loss of income due to ill health and increased medical costs. Chronic smoking-related structural decreases in vmPFC, insula and thalamus have been observed and overlap with regions showing acute nicotinic drug-induced functional modulations. These findings highlight the relevance of thalamic gating and cortico-striatal pathways subserving behavioral regulation and reward in the maintenance of nicotine dependence.
Table of Contents
Putamen
The putamen contains neurons that release the neurotransmitter GABA and sends pathways to other regions of the basal ganglia, including the globus pallidus and the substantia nigra. These circuits allow for cortico-subcortical communication, and the putamen transmits GABA to modulate other neurotransmitters involved in movement and decision-making (including enkephalin, substance P, and acetylcholine). The brain area of the putamen is also implicated in the development of addiction. However, what part of the brain does tobacco affect? In a series of studies, researchers found that putamen is associated with craving and addiction in people who smoke cigarettes.
Moreover, the putamen is related to motivational and emotional responses to smoking, such as pleasure, negative affect, and anxiety. Using meta-analytic techniques, researchers found that chronic smoking is associated with concurrent structural decreases in GM and WM across multiple studies in vmPFC, insula, and thalamus. These results indicate that smoking affects the integrity of functionally interrelated neurocircuits involving the reward, impulsive, and emotional control systems. Additionally, research suggests that smokers experience more cognitive decline than non-smokers. Specifically, a picture vocabulary test was used to determine the level of cognitive impairment, and the results show that participants who reported ever-smoking exhibited lower scores than non-smokers. In addition, the results showed that the volume of the right inferior frontal gyrus, the right/left insula, the left middle frontal gyrus, and the right cerebellum anterior lobe were significantly correlated with pack years and the FTND score.
Prefrontal Cortex
The prefrontal cortex is a hub of neurobiological activity related to executive function and self-control. Chronic nicotine exposure has been linked to deficits in attention and memory and is associated with structural alterations in the prefrontal cortex. These structural alterations may have functional implications as the prefrontal cortex is involved in behavioral responses to acute nicotinic drug administration, including nicotine craving. Structural alterations were observed in both GM and WM in smokers compared to non-smokers, particularly in GM areas of the precuneus, superior and middle frontal gyrus, insula, and posterior cingulate and WM areas of the precentral and caudal middle temporal gyrus and cerebellum anterior lobe. Most between-group abnormal regions significantly correlated with pack-years and FTND scores in the regression analyses. Still, none of the clusters were associated with the cognitive performance measures. Smokers exhibited lower surface area in both brain hemispheres, as measured by total cortical surface area at wave one and cortical volume at follow-up. Additionally, rCBF was lower in the tobacco ever-user group at the left inferior frontal gyrus and in banks of the superior temporal sulcus, medial orbitofrontal gyrus, and caudal middle temporal sulcus, as well as in the dorsal anterior cingulate and right hippocampus, and cigarette craving scores correlated with rCBF changes in these regions.
Posterior Cingulate Cortex
The posterior cingulate cortex (PCC) is a crucial center in the default mode network responsible for various cognitive and behavioral processes. The PCC is also linked to numerous psychiatric disorders, such as depression, anxiety, addiction, and schizophrenia. However, more knowledge is needed concerning the PCC’s particular state-specific functional activity patterns. This is because recent dual-analytic approaches such as meta-analytical connectivity modeling (MACM) and high-resolution resting-state fMRI have only recently identified separate PCC activation and deactivation patterns among smokers. These MACM analyses quantified the degree to which individual structurally impacted ROIs overlapped with one another with healthy controls if an ROI’s MACM map exhibited at least 50 voxels of overlap with the MACM maps of other structurally affected ROIs, those two regions were considered to interact and to be part of a neurocircuit. Several studies have reported that smoking is associated with decreased gray matter density in the pregenual anterior cingulate cortex (ACC, areas 25, s24, and s32). This region may represent a value representation and is involved in decision-making. For example, it is activated by odor pleasantness and unpleasantness stimuli and monetary reward outcomes. It is also involved in the regulation of emotions. It is connected to the hypothalamus and brainstem autonomic regions, suggesting that it is involved in the autonomic components of emotion.
Thalamus
The thalamus is a part of the diencephalon, the embryological precursor to the brain. It is a critical component of the climbing system and has connections with cortical areas such as the prefrontal cortex and striatum. The thalamus is also involved in memory processing and attentional control. The alterations in thalamic nuclei caused by nicotine use are likely related to these cognitive deficits. In one study, rCMRglc, an indirect measure of neuronal activation, was correlated with normalized rCBF (another indirect measure of neuronal activation) in the thalamus to determine whether rCBF captures the same information as rCMRglc. In this experiment, rCBF correlated with cue-induced craving in smokers and non-smokers. In this region, smokers showed greater rCBF responses when they perceived the cue to be a cigarette than non-smokers. The thalamus is rich in nicotinic receptors and is associated with the motivation to engage in drug-seeking behavior. The thalamus is also important for emotional processing, and the medial prefrontal cortex (mPFC) and insula regions have been implicated in emotion regulation and face processing. The smokers’ l alterations observed in smokers’ mPFC and insula regions are likely related to disrupted emotional processing and law in these individuals, as well as a decreased ability to self-regulate negative emotions such as those experienced during smoking.
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