Complete data required for functional connectivity analyses were available from 216 fMRI scans across placebo and alcohol challenge sessions for 108 individuals. The subjects were comprised of 54 pairs of low- and high-LR participants who were matched on sex, demography, drinking frequency and usual quantities, as well as tobacco and cannabis use. The data presented here were extracted from the Hariri emotional face recognition task, which was presented to participants in the MRI scanner 60 min post-beverage consumption during placebo and alcohol fMRI sessions. The task was measured at a time close to the peak BrAC during the average alcohol session. At this point of the alcohol session, the alcohol levels were similar in the LR groups.We used a modified version of the Hariri emotional face-processing task . Participants were presented with a target face and two probe faces for 5 s, with instructions to match the probe and emotional expression of the target by pressing a button in a block design. Each block had six consecutive trials where faces were either angry, fearful, or happy. Additionally, a sensorimotor control condition was used where vertical or horizontal ovals or circles were presented for six consecutive trials in block with instructions to match the shape of the probe to the target. Each block of emotion condition and the sensorimotor control condition were presented three times in a pseudorandomized order. The task began with an 8-s fixation period and had interspersed 12-s fixation periods between each block. There were 18 trials for each condition yielding 512 s total task time. Figure 1 illustrates the timing of the task with examples from the first two blocks .
We recorded accuracy and reaction time during the task to confirm the task was carried out correctly .To correct for small movements over time,ebb and flow grow table image repetitions were registered to a selected base volume via AFNI’s 3dvolreg program. The time series of the motion parameters were used in the linear regression analysis of individual data to control for spin history effects . Functional data were then transformed into the participant’s anatomical space and aligned to standard space using the previously computed anatomical transformation matrix and smoothed with a 4-mm FWHM Gaussian kernel. Deconvolution analysis of the fMRI time series data was conducted using AFNI’s 3dDeconvolve algorithm. The general linear models used reference vectors for the task conditions convolved with the hemodynamic response function. Estimated motion and linear, quadratic, and cubic trends were also included as nuisance variables. The resulting model generated scaled beta coefficient maps representing the mean percent BOLD signal change for each condition of the task relative to baseline.During angry faces, using the left amygdala seed, the differences between low and high responders illustrate that low LR participants had lower functional connectivity in several cortical regions compared with high LR participants in both placebo and alcohol conditions. This was observed in the left medial frontal gyrus, bilateral ventral anterior cingulate, bilateral posterior cingulate, and left supramarginal gyrus. Using the right amygdala seed, the main effects of LR during processing of angry faces were identical to left amygdala such that low LR participants had diminished functional connectivity as compared to high LR participants in both placebo and alcohol conditions in the bilateral posterior cingulate.
In contrast, during happy faces, significant effects were observed only with the right amygdala seed where, opposite to the LR main effects pattern observed for angry faces, low LR participants had greater functional connectivity compared with high LR participants in the right dorsal anterior cingulate gyrus and right caudate.During angry faces, within the right precuneus, lower functional connectivity was observed with the left amygdala following alcohol compared with placebo in low LR individuals, but increased connectivity following alcohol was found in high LR individuals. Interactions during processing of happy faces were characterized as a decrease in functional connectivity with right amygdala following alcohol as compared to placebo in low LR individuals, but increased connectivity following alcohol in high LR individuals in left middle frontal gyrus regions; a pattern similar to the interaction observed during angry faces.Given that we had 5-year follow-up data on these participants , we conducted post hoc exploratory regression analyses examining if regions with significant functional connectivity differences predicted a change 5 years later in drinking quantity or the subsequent development of alcohol problems in low versus high LR individuals. Two regions during the placebo condition significantly predicted an increase in alcohol problems for low LR participants: the right dorsal anterior cingulate gyrus during happy faces ; and the bilateral posterior cingulate gyrus during angry faces . For both regions, greater decreases in amygdalar functional connectivity during placebo was associated with an increase in future alcohol problems.The main goal of these analyses was to expand upon the findings of Paulus et al. by evaluating LR group differences in functional connectivity. This is the first demonstration of differences in connectivity between low and high LR individuals, results that might help explain why drinkers with low LRs might require greater cognitive effort to perform optimally on some tasks.
Consistent with our hypotheses, in the current analyses the most prominent patterns found were attenuation of amygdala connectivity with cortical regions in low LR participants, both during placebo and in response to alcohol, relative to high LR participants while viewing angry faces. Additionally, comparing alcohol and placebo sessions, low LR individuals exhibited decreased functional connectivity in response to alcohol, whereas high LR individuals showed increased functional connectivity while viewing both angry and happy faces. The present findings add to the regional brain changes originally reported by Paulus et al. . While those authors found no difference in amygdala regional activation patterns across LR groups, we found several differences in functional connectivity with the amygdala that varied depending on the valence of facial affect being decoded. Thus, BOLD signal changes in the cortex in response to an emotional processing task in low versus high LR individuals might reflect aberrant functional connectivity in corticoamygdalar circuits. These functional connectivity differences were observed in relatively highly functioning individuals from a nonclinical sample, some of whom carried an enhanced risk for alcohol problems through a low LR but none of whom had yet developed an AUD. Along with a growing body of evidence that the low LR phenotype is characterized by CNS differences relative to their high LR peers , these emotional processing data suggest that low LR individuals may have an altered neurobiological process in which they recognize some negative or positive social cues through decoding facial affect. It is also possible that given the pattern of brain regions in the frontal lobe,flood and drain table grow anterior cingulate, and insular cortex that showed altered amygdala functional connectivity, as well as regional BOLD signal changes in theinsula, low LR individuals may have an impaired ability to recognize intoxication, or the rewarding aspects of alcohol, in social situations. Functional connections between the amygdala and cortical regions play important roles in processing human emotions. For example, connections between the PFC and amygdala facilitate the cortex’s top-down regulation in decoding emotional stimuli , allowing appraisals based on affective information to moderate goal-directed behaviors . PFC-amygdala functional interactions are reciprocal and likely necessary to process socially based emotional signals to generate an emotional response . Additionally, connections between the amygdala and insular cortex have been shown to be involved in the interoceptive processes involved in recognizing intoxication . That finding supports our interpretation that low LR individuals may have an impaired ability to recognize the effects of alcohol at the moderate doses used in our challenge paradigms.
It is interesting to note that the findings of low LR-related lower connectivity between the amygdala and cortical region pathways observed with angry faces were not seen in the reaction to fearful faces. While similar in that both are negatively valenced emotions, fearful and angry emotional responses regulate the stress response in specific adaptive ways with different biological profiles. For example, when responding to a psychosocial stressor , angry reactions to stress lead to greater increases in cortisol over time but not to elevations in pro-inflammatory cytokines. In contrast, fear reactions to stressors lead to increases in proinflammatory cytokines over time and decreased cortisol . Therefore, our findings of altered functional connectivity needed to process anger in low LR individuals are consistent with the perspective that distinct emotional experiences trigger specific adaptive biological processes. Another finding of interest relates to happy faces. Here, we also observed an opposite main effect pattern such that low LR participants had greater functional connectivity between the amygdala and anterior cingulate as compared to high LR participants across both placebo and alcohol. Positive emotions often elicit activation in the brain’s reward circuitry and future studies should examine if the LR group patterns related to happy faces are also related to future problematic drinking and the development of AUD. Regional brain differences, especially in the anterior insula and frontal gyrus, predicted future problems with alcohol 5 years later in this sample . In our post hoc exploratory analyses, lower cingulate-amygdala functional connectivity during the placebo condition among low LR individuals significantly predicted an increase in alcohol problems 5 years later. Given the exploratory nature of these analyses, and that we did not correct for multiple tests, caution should be applied in interpretation of these post hoc findings. Nonetheless, they do suggest that LR-specific functional MRI findings may be predictive of future alcohol problems and additional research is needed in this area. In viewing the current results, it is important to keep some limitations in our research protocol in mind. First, the participants were all relatively stable and functional European American university students, and it is not clear whether the current results generalize to other groups. Second, consistent with the results reported by Paulus et al. and most of our prior papers, in order to place LR into a more useful clinical context LR was evaluated as a dichotomy, and examination of LR-derived scores as a continuous variable may yield additional findings. Third, reflecting the fact that laterality findings are unclear in many fMRI studies of emotion , we analyzed the combination of both the left and right amygdala seeds and their respective connectivity patterns. Thus, future work will need to further evaluate the importance of laterality influencing connectivity patterns associated with the low LR. Fourth, our analyses focused on the whole amygdala and not amygdalar sub-regions, and future work will be needed to expand upon the analyses presented here . Fifth, there are physiological effects when consuming alcohol that directly impact the BOLD signal, such as cerebral blood flow changes . With advances in neuroimaging methodologies, future studies can be done isolating mechanisms that drive BOLD signal changes observed in the literature including blood flow, volume, and oxygenation. Sixth, only 18 trials per emotional face were used in the current protocol yielding a task time of 512 s, which may have limited statistical power given concerns for task-based fMRI reliability.Seventh, gPPI analyses are correlational and, therefore, directionally between the amygdala and other regions cannot be inferred. Future studies on dose-dependent effects of alcohol are needed to make causal inferences, and it would be interesting to examine other important brain regions as gPPI seeds. Finally, regarding the post hoc exploratory analyses linking some of the functional connectivity findings with the development of future alcohol problems, these results should be considered tentative until tested more directly in future research. In summary, building upon prior findings of regional brain LR group fMRI differences in frontal and insular cortices , we demonstrate that low LR individuals have amygdala connectivity differences relative to high LR individuals. These findings add to a growing body of fMRI studies that show regional brain characteristics in low LR individuals and demonstrate how amygadla-dependent functional connections may play a role in those characteristics. Attenuated connectivity among low LR individuals may contribute to an impaired ability to recognize developing alcohol intoxication in social situations and impaired ability to make appraisals of angry and happy emotions irrespective of consuming alcohol.Opiate drugs, especially heroin, have been the primary type of illicit drug used in China since the 1980s .