Neuromelanin contributes to locus coeruleus contrast in MRI scans

The locus coeruleus (LC) attention system is a target for understanding cognitive difficulties in children and older adults. Recent neuroimaging studies have suggested that LC can be structurally identified.  We now have direct evidence from an ex vivo imaging and histologic study that this contrast is impacted by the density of neuromelanin that normally accumulates in LC neurons with age (picture below: neuromelanin across histological sections corresponds to contrast in the MRI scan).  It is not clear that there is a direct correspondence between LC contrast, neuromelanin, and the number of healthy LC neurons, but the demonstration that neuromelanin contributes to LC contrast in MRI scans is a first step in  developing a biomarker that could be used to track disease and benefit from interventions.


Cingulo-opercular Activity Provides Word Recognition Benefit


Recognizing speech in challenging listening conditions often produces increased activity in frontal cortex, particularly in cingulo-opercular regions, but the significance of this activity has been unclear.  This network of frontal cortex is thought to monitor performance and signal when cognitive resources are required to ensure successful performance.  Findings from earlier visuospatial studies indicated that cingulo-opercular activity can be predictive of performance on the next trial, so we investigated whether cingulo-opercular activity could also predict word recognition when words were presented in a multi-talker babble.  The results of our fMRI experiment demonstrated that elevated activity in cingulo-opercular cortex provided word recognition benefit on the following trial.  While elevated cingulo-opercular activity was not necessary for word recognition, up to 13% more words were recognized when activity was high compared to when it was low suggesting that elevated activity provided for optimal word recognition.  These results are important because they support the premise that cingulo-opercular activity can enhance ongoing task performance and does not only reflect difficulty or error.  They also suggest the intriguing possibility that we can enhance our performance on a variety of tasks and especially speech recognition by engaging cingulo-opercular cortex.  These findings have been published in the Journal of Neuroscience.


Changes in the Brain that Occur with Hearing Loss

Age-related hearing loss occurs for just about everyone.  We wondered about the potential impact of hearing loss on brain structure because speech recognition can be difficult even after correcting for poor hearing thresholds.  In a sample of 49 older adults, we observed that high frequency hearing loss was associated with lower gray matter volume in auditory cortex.  Importantly, Dr. Kelly Harris from our Hearing Research Program has observed that individual differences in auditory cortex structure relates to individual differences in hearing thresholds even before hearing loss is considered clinically significant. These findings emphasize the importance of protecting your hearing and suggest that starting to wear hearing aids as early as possible may limit potential changes in brain structure.

But what about low frequency hearing?  In a follow-up study of 72 older adults, we tested a long-standing hypothesis that low frequency hearing loss occurs with vascular disease affecting vessels supporting the cochlea and the brain.  We examined the extent to which evidence for small vessel disease in the white matter of the brain was associated with low frequency hearing thresholds in older adults.  Variation in frontal white matter was related to low frequency hearing variation in women and people with a history of high blood pressure.  These results suggest that people with high blood pressure are at risk for low frequency hearing loss.  Future studies are necessary to determine if these findings can be explained by how well high blood pressure is controlled and/or the duration of high blood pressure before people seek treatment, for example.

Missingness in fMRI Studies: Multiple Imputation

Limited imaging coverage of the brain and susceptibility artifact contributes to missing data in functional imaging studies.  Multiple imputation is one solution for dealing with missing data.  We demonstrate in a recent Neuroimage manuscript the considerable benefit of using multiple imputation in functional imaging studies. There was a 35% increase in the number of voxels that were analyzed in a group study when multiple imputation was used to “fill in” missing data.  This approach will help to reduce the number of false negative results, increase power, and increase the validity of whole brain studies, particularly those involving large open access databases and ultra high-field imaging.