Amygdala involvement in human avoidance, escape and approach behavior Page: 4
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Schlund and Cataldo Page 4
money loss actually remained aversive throughout the task and loss was not overshadowed by
earnings. Pretraining continued until response accuracy exceeded 90% during two consecutive
blocks of 20 trials for each contingency. Response accuracy was defined as earning >90% of
Z available reinforcers to the approach cue, avoiding >90% of losses to the avoidance cue,
escaping >90% of the total programmed loss to the escape cue and not emitting any responses
to the punishment cue.
c Subjects were not informed about cue-response-outcome contingencies but were told that their
task was to earn as much money as possible, with 100% accurate performances producing the
maximum of $60.00 (the range of earnings was $58-$60). Subjects were also not informed of
the minimum response requirement for each contingency. The rationale for not imposing an
upper limit on the number of responses was to obtain measures of approach, avoidance and
escape motivation with greater responding providing a index of greater motivation. Our
O. rationale for using a larger amount of money for approach relative to avoidance and escape is
based the suggestion that the magnitude of the response to negative stimuli is often larger than
to positive stimuli which necessitated a larger reward to decrease the potential imbalance
(Baumeister et al., 2001).
fMRI task and acquisition
Three -14 minute imaging runs were completed. The imaging task employed the same trial
Z structure and timing parameters used during training and involved presenting each cue-
contingency (approach, avoidance, escape and punishment) and the baseline cue for 15 trials
within an event related design. Responses were made on a hand-held button box containing
Three response buttons arranged vertically and labeled 1, 2, and 3. Instructions emphasized that
the task was identical to the training task. Functional MRI images were collected on a 3 T
Philips scanner at the F. M. Kirby Research Center for Functional Neuroimaging. T1 weighted
o anatomical volume images were collected for each subject using a MPRAGE sequence with a
high-resolution isovoxel acquisition of lmm3. Functional MRI data were gathered using a
single shot echo planar imaging (EPI) sequence with a TR of 2 s, a TE of 30 ms, a 90 degree
c flip angle, 128 x128 matrix size and field of view 24 cm, yielding voxels measuring 3x3 mm
o in plane. Approximately 43 contiguous 3 mm thick sections were obtained. The first three
-0 volumes were discarded to allow for equilibration effects. Functional images were first
reconstructed from k-space to image space for further processing.
Data analysis was performed using Statistical Parametric Mapping software (SPM 2). For a
subject's imaging data to be included in the analysis, head movement was limited to less than
2 mm. Preprocessing procedures included reorientation, slice acquisition time correction,
Z coregistration, within-subject realignment, spatial normalization to the standard Montreal
= Neurological Institute EPI template, resampling to 2mm3 voxel size, and spatial smoothing
using a Gaussian kernel (6 mm fullwidth at half-maximum). High pass filtering was applied
to the time series of EPI images to remove any low frequency drift. A canonical hemodynamic
c- response function was used as a covariate in a general linear model and parameter estimates
o were generated for each voxel that corresponded to the onsets of cues and subsequent outcomes.
" Parameter estimates derived from the mean least squares fit of the model to the data reflect the
Strength of covariance between the data and the canonical response function for our events of
interest. Separate contrast images were generated by contrasting activation associated with
Co each condition cue relative to the baseline cue. Images were carried to a second-level group
". analysis which treated intersubject variability as a random effect. Voxel-wise comparisons
were performed within a repeated measures analysis of variance to identify voxels with
significant activation relative to baseline, with post-hoc paired t-tests performed to identify
Significant differences in activation between conditions. The statistical thresholds used for
Neuroimage. Author manuscript; available in PMC 2011 November 1.
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Schlund, Michael W. & Cataldo, Michael F. Amygdala involvement in human avoidance, escape and approach behavior, article, November 1, 2010; [Amsterdam, Netherlands]. (digital.library.unt.edu/ark:/67531/metadc77178/m1/4/: accessed March 28, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT College of Public Affairs and Community Service.