Examining the Relationship between Impulsive Personalities and Neural Functioning in Cocaine-Addicted Participants

BACKGROUND: Those who suffer from addiction are unable to discontinue use despite serious consequences affecting their social, professional, and family lives. Individuals who suffer from the disorder often alienate themselves from loved ones and lose their jobs. Addiction involves continuing a behavior despite severe negative consequences. Numerous studies have identified a relationship between impulsivity and the development of substance abuse. This study examines the relationship of impulsive personality facets and neural functioning associated with inhibition.

SUBJECTS: The study sample included 24 healthy control participants and 56 cocaine-addicted participants. Participants ranged in age from 25 to 54 years old with a mean age of 43.27 (±SD 7.84). The group was comprised of 68 male and 12 female participants, 28.7% self identified as Caucasian, 66.3% African American, 3.8% Hispanic, and 1.3% Asian/Other. Healthy controls and cocaine-addicted participants were similar in age and race but differed in gender (p= .02). The control group had 17 males and 7 females while the cocaine-addicted group had 51 males and 5 females.

METHODS: Demographic information was gathered for all participants. Each participant also completed a Neuroticism Extroversion and Openness (NEO) personality measure and Temperament and Character Inventory (TCI), Structured Clinical Interview for DSM-IV (SCID), Wechsler Test of Adult Reading (WTAR). They then performed the stop signal task (SST) during functional magnetic resonance imaging (fMRI) to gather data on neural activation during Stop-Success (SS) and Stop-Failure (SF). fMRI data was analyzed using FSL imaging software. All statistics were run with SPSS software. Functional ROIs were identified and analyzed in fMRI Expert Analysis Tool query (FEATqueary) to gather data on each participantÕs change in blood oxygen level dependent (BOLD) activation during Stop-Success (SS) and Stop-Failure (SF). Impulsive personality facets were then used to identify relationships between BOLD activations of the ROIs.

RESULTS: Between group comparisons found significant differences in mean scores on all of the impulsive personality facets except for Exploratory Excitability and Persistence from the TCI, and Excitement Seeking from the NEO. Neuroimaging results are similar to other studies utilizing the SST finding changes in activation of the middle frontal gyrus, superior frontal gyrus, cingulate gyrus, medial frontal gyrus, insula, caudate and supramarginal gyrus during Stop-Failure; and superior parietal lobule, middle frontal gyrus, precuneus, supramarginal gyrus, inferior temporal gyrus, and middle occipital gyrus during Stop-Success. However, no differences in BOLD activation between groups were observed. Numerous relationships were identified between the personality facets and BOLD activation of the regions of interest (ROIs). To further elucidate this relationship between neural functioning and personality a principal component analysis (PCA) was conducted on all eleven personality facets. The PCA allowed for the identification of an impulse control personality component and an impulse drive personality component. A significant interaction with the impulse drive and the left posterior hippocampus was identified.

DISCUSSION: This study allowed for the examination of how impulsive personality facets relate to, or interact with, neural functioning during a task designed to measure inhibition. Despite failing to find a difference in activation of the ROIs between cocaine-addicted participants and healthy controls, the study successfully identified the cocaine-addicted group to have a significantly more impulsive personality than healthy controls. It also identified numerous relationships between the personality facets and neural functioning. This gives credence to the idea that neural functioning and personalities are associated in some way. Reverse relationships were observed between the groups in the relationships between the Impulse Drive personality component and SF activation of the hippocampus; and the TCI facet of Purposefulness and SS activation of the right thalmus. These reverse relationships may signify a difference between the groups that may either predispose the cocaine-addicted participants to developing substance abuse, or it may be a neuro-functional change that has resulted due to prolonged exposure to cocaine.