Loss of laterality in chronic cocaine users: an fMRI investigation of sensorimotor control

Abstract

Movement disturbances are often overlooked consequences of chronic cocaine abuse. The purpose of this study was to systematically investigate sensorimotor performance in chronic cocaine users and characterize changes in brain activity among movement-related regions of interest (ROIs) in these users. Functional magnetic resonance imaging data were collected from 14 chronic cocaine users and 15 age- and gender-matched controls. All participants performed a sequential finger-tapping task with their dominant, right hand interleaved with blocks of rest. For each participant, percent signal change from rest was calculated for seven movement-related ROIs in both the left and right hemisphere. Cocaine users had significantly longer reaction times and higher error rates than controls. Whereas the controls used a left-sided network of motor-related brain areas to perform the task, cocaine users activated a less lateralized pattern of brain activity. Users had significantly more activity in the ipsilateral (right) motor and premotor cortical areas, anterior cingulate cortex and the putamen than controls. These data demonstrate that, in addition to the cognitive and affective consequences of chronic cocaine abuse, there are also pronounced alterations in sensorimotor control in these individuals, which are associated with functional alterations throughout movement-related neural networks.

Figure 1. Finger-tapping task

In the functional MRI scanner all participants were instructed to mimic movies of unpredictable finger-tapping sequences with their dominant right hand (A). These 30s task blocks were interleaved with 30s rest blocks and 9s motor preparation periods for each functional run (B). All participants performed two functional runs of the task.

Figure 2. Task Performance

Mean (with standard error) reaction time (a) and number of errors (b) on the finger-sequencing task for cocaine users (solid) and matched control participants (lined). * p<0.05, ** p<0.01, ***p<0.00001

Figure 3. Distribution of brain activity during right-hand finger tapping

Voxel-based maps of significant brain activity for controls (A) and chronic cocaine users (B). To extend the data analysis beyond motor-related regions of interest, contrast maps were made for each individual comparing brain activity associated with performing the task to periods of rest. These data were modeled across all subjects in order to get a voxel-based representation of brain areas being used to perform the task for each group. To determine the areas significantly activated during the task relative to rest for each subject a minimum cluster size was set at 25 voxels with a threshold of statistical significance was set at p < 0.005 for uncorrected values.

Figure 4. Activity in motor related regions during right-hand finger tapping

Percent signal change in the contralateral hemisphere (black) and the ipsilateral hemisphere (gray) of controls (a) and cocaine users (b). Significance is indicated for brain regions that differ significantly between hemispheres within each group (* p<0.01, ** p<0.001) and within hemisphere between groups (# p<0.01, ## p<0.001).

Figure 5. Degree of functional laterality for motor-related regions of interest

The laterality index (LI) for each region of interest is plotted for both controls (lined) and cocaine users (solid). A positive LI means that activity is lateralized to the left hemisphere, while a negative LI indicates right sided laterality. Brain regions with significant between group differences are indicated with asterisks (* p<0.05).