We used deformation-based morphometry to examine brain structure differences between 1-week-abstinent alcoholics and light drinkers, and to compare tissue recovery over several months in abstinent alcoholics to normal aging. The major findings of this study are: 1) alcohol dependence in this predominantly male Caucasian cohort is associated with significant reductions of tissue in foci within the frontal and temporal lobes, 2) heavier drinking is associated with greater tissue losses in the frontal and temporal lobes, although these relationships were not significant after extensive correction for computing statistics at every voxel, 3) RA with at least two months of abstinence demonstrated greater tissue gain throughout the brain than LD or RA who consumed alcohol within 15 days of their follow-up MRI, and 4) tissue recovery for RA as a group was significantly related to GM volume at 1 week of abstinence, but not to WM volume at 1 week of abstinence or to previous drinking severity.
DBM is perfectly suited to visualize brain shape differences between groups, changes over time related to the effects of alcoholism or abstinence on the brain, and to highlight patterns of altered brain structure related to these conditions. The cross-sectional findings expand on previous reports of cerebral abnormalities in chronic alcohol exposure, in that they localize the specific pattern of cerebral dysmorphology. We observed tissue loss in RA in all lobes of the brain, as reported previously using conventional lobar volume measures in treatment-naïve heavy drinkers and in treatment-seeking alcoholics. However, using DBM, only foci in the frontal and temporal lobes reached significance after correction for multiple comparisons. These findings could arise if alcohol leads to spatially diffuse tissue loss that varies across participants, since DBM is best suited for discerning focal losses of brain tissue that occur consistently from one participant to the other in similar brain regions (i.e., spatially consistent). Alternatively, the magnitude of losses in non-significant brain regions may be small, and we do not have the power to detect significant changes.
In this RA cohort, volumes of caudate, putamen, or nucleus accumbens were not significantly reduced as has been previously reported in alcoholics (Sullivan et al. 2005
). This may in part be due to imperfect registration of these structures. The sensitivity of crosssectional DBM to detect changes is reduced in regions of high anatomical variability which prevent the estimation of a true one to one mapping between MRI scans of a subject (for example where there are different numbers of sulci and gyri), and may be visualized as blurrier regions in the average spatially normalized image (see and ). We have implemented automated atlas-based voluming of the caudate, lenticular nuclei, and thalami based on the between-subject registration methods used in this study. In previous work, we showed this automated method had comparable reliability to between-rater manual delineation (Cardenas et al. 2005
), but performed least accurately identifying the caudate. If the caudate nuclei were imperfectly registered in our RA, then any tissue contraction reflected in the Jacobian would not consistently map to the same location within the common coordinate system, and our ability to detect volume reductions in RA would be compromised. Alternatively, the filter width used to smooth our Jacobian maps (15 mm) may not have been optimal for detecting atrophy in very small structures such as the nucleus accumbens, reducing the sensitivity of DBM to detect change. Although our previous work has shown that this filter width is optimal for valid estimation of left temporal lobe gyral tissue volumes (Studholme et al. 2004
), it may not be optimal for other regions of the brain. In general, the optimal filter width is related to the spatial scale of the effect. For example, large filter widths optimally detect diffuse effects throughout a major lobe, and may blur very focal effects. Investigation of a range of filter widths may reveal other regions of the brain with alcohol-related atrophy.
Within the RA, frontal and temporal lobe volumes were inversely related to measures of alcohol consumption, though not statistically significant after correction for multiple comparisons. This general pattern suggests that greater consumption of alcohol is associated with greater dysmorphology. In a previous DBM study of active heavy drinkers with alcohol use disorders (Cardenas et al. 2005
), we only observed association between frontal GM and drinking severity. The RA participants in this study drank nearly twice as heavily in the year prior to study as the active heavy drinkers in our previous study, and it is possible that the temporal region is only affected under this significant level of alcohol consumption. In other words, our results suggest that the frontal lobe is most vulnerable to the effects of heavy chronic alcohol consumption, whereas other brain regions are only affected with more severe drinking levels.
We measured the change in brain volume over time directly by registering images acquired at two time points and evaluating properties of the transformation. Because of the similarity between scans of the same subject, the registration process is simplified, resulting in increased sensitivity and accuracy of longitudinal DBM to capturing change within a subject. When compared to normal aging (i.e., longitudinal tissue change in LDs), RA, as a group, showed greater tissue volume increase over time in many regions throughout the brain, including the frontal lobe and cerebellum, parts of the fronto-ponto-cerebellar circuitry that were hypothesized to be affected by heavy drinking (Sullivan 2003
), and are implicated in executive functions, learning and memory, in addition to postural stability and gross and fine motor functions (Sullivan et al. 2005
). Most of these regions did not survive correction for multiple comparisons, however, so we compared RA who maintained sobriety to those who relapsed, assuming that relapse would impede tissue recovery. The regions of significantly greater tissue recovery encompassed by contour lines in generally include the same lobar regions shown to recover in our preliminary volumetric ROI analyses of a similar patient cohort (Gazdzinski et al. 2004
), and would be consistent with earlier studies that report improvement in global measures of brain volume during abstinence. also displays relatively large colored regions of the images that are not circumscribed by contour lines prescribing significant clusters (e.g., subcortical structures, deep white matter, particular lobules of vermian regions), where the magnitude of tissue gain may be small and we lack the power to detect significant changes. Longitudinal DBM can probe for small-scale changes in local brain volume and separate them from local effects of tissue displacement that can confound techniques such as the boundary shift integral (Boyes et al. 2006
). Because of this advantage, DBM adds significant value over conventional methods that previously looked for longitudinal changes in the brain globally or in specific regions, which may not conform to the actual pattern of effect present in the brain. There is also great value in the new hypotheses that are generated based on the results from DBM analyses, such as greater tissue recovery in subcortical structures, that can be used to guide new research.
The findings that brain tissue volume recovers during abstinence and is impeded by relapse are somewhat weakened by our sample size and our definitions of ReRA and AbRA. Our 17 AbRA had maintained uninterrupted sobriety for at least two months before followup; however, 5 of them had a brief episode of drinking between scans. Our ReRA group consisted of recent relpasers, who had consumed alcohol between 1 and 15 days before followup MRI, with the amount of alcohol consumed and the duration of the relapse episode rather variable. The influence of these factors on tissue recovery is unknown and can only be addressed in significantly larger homogeneously relapsing populations.
Within the RA, we examined whether measures of drinking severity and tissue volume at 1 week of abstinence were related to subsequent tissue recovery during abstinence. Our reasoning was based on previous observations by others and us (Pfefferbaum et al. 1995
; Gazdzinski et al. 2005
) that those with the greatest deficits at 1 week of abstinence (due to heaviest drinking or as indexed by tissue atrophy) might show the greatest recovery. Heavier drinking before alcoholism treatment was not strongly related to subsequent tissue recovery. Tissue recovery per se and its correlation with greater drinking severity may be limited to a relatively young alcoholic population with enough residual neuroplasticity (e.g., local increases of dendritic branching and/or myelin density) to allow appreciable tissue volume increase with prolonged abstinence from alcohol. We found significant relationships between volume of GM at 1 week of abstinence and tissue recovery in the frontal, temporal, and cingulate GM. WM volume at 1 week of abstinence was not related to tissue recovery in any region. This suggests that GM atrophy at entry into alcoholism treatment predicts volume recovery during abstinence better than WM volume at entry. Regression toward the mean is another possible but unlikely interpretation for this finding, since we have previously shown that the errors in DBM-derived volume measurements (compared to manual tracing) are small in comparison to normal subject measurement variability (Studholme et al. 2004
In this DBM study, the baseline deformation and longitudinal deformation maps were derived from different registration methods. Spatial normalization between subjects, and registration to track change over time within a subject, are two very different registration tasks. We used a fluid registration within subject over time in order to capture subtle sub-voxel changes in tissue boundaries. Although fluid registration can also capture large scale changes, it is prone to problems of stability, allowing large scale flows to occur when estimating mappings between different subjects. We have therefore used B-Spline based deformations in this study for the process of spatial normalization and cross-sectional morphometry. We have applied identical spatial filtering for both analyses to remove ambiguities in the location of size differences or changes due to spatial normalization. Because the spatial normalization process and analysis was identical for all subjects, there should be no significant effects on the mapping and no bias in the group comparisons due to using different registration methods.
In conclusion, DBM is useful for visualization and quantitation of brain shape differences between alcohol-dependent samples and light drinking controls as well as for demonstration of structural alterations during abstinence from chronic alcohol consumption. The results expand on previous observations and complement previous volumetric evaluations of ROIs by these and other investigators. Future work will expand the use of DBM to alcoholic subpopulations (e.g., smokers), investigation of tissue recovery as it relates to regional GM and WM volumes, and examination of brain anatomy underlying neurocognitive deficits observed in recovering alcoholics.