Page 60 - NNS 2014 Program & Abstract Book

movement interference and data were band-pass filtered in delta
(0.75–4 Hz), theta (4-7 Hz), alpha (8-13 Hz), beta (16-24 Hz) and
gamma (25-40 Hz) frequency bands. Cortical surface was determined
from MR T1 images using FreeSurfer. The cortical distribution of the
mean signal power in each frequency band was estimated and inte-
grated over 68 cortical regions (Desikan-Killiany atlas), and the re-
gional power was contrasted between groups.
Increased delta oscillatory activity was observed in Group 1 in
bilateral regions of the medial temporal lobe (entorhinal and para-
hippocampal cortex, and isthmus of the cingulate gyrus). Increased
gamma activity was also observed in visual cortical areas. A decrease
in theta and alpha activity was observed in Group 1 in regions of the
left inferior frontal gyrus, and left lateral temporal cortex.
Our observations support a neurobiological model that posits hy-
peractivity in regions of the limbic system in patients with PTSD,
accompanied by low oscillatory activity in frontal and temporal brain
regions that can have a role in the regulation of the limbic system
reactivity.
Key words
magnetoencephalography, MRI, mTBI, PTSD
A2-11
NETWORK-BASED ANALYSIS OF STRUCTURAL CON-
NECTIVITY REVEALS ALTERED BRAIN ORGANIZATION
AFTER EXPERIMENTAL BRAIN INJURY
Harris, N.G.1, Verley, D.R.1, Brown, J.A.2
1University of California, Los Angeles, Los Angeles, USA
2University of California, San Francisco, San Francisco, USA
Altered axonal integrity is a well-known marker of traumatic brain
injury that can be visualized by diffusion tensor imaging (DTI). Our
prior studies in the rat controlled cortical impact (CCI) model indicate
that tract-based statistical analysis (TBSS) of DTI data underestimates
the extent of axonal injury when compared to silver-staining histo-
chemical studies of other labs. We tested whether a quantitative
analysis of DTI-based brain networks would provide a more sensitive
indicator of axonal damage and if alterations in network connectivity
might also underlie TBI dysfunction. We employed TBSS and graph
theory measures of brain connectivity to assess DTI data acquired
before and at 28 days after moderate CCI-injury in rats (n = 17). TBSS
revealed alterations in fractional anisotropy, radial, axial and mean
diffusivity that was restricted to the ipsilateral corpus callosum
(P < 0.05). Network analysis revealed a trend towards globally in-
creased characteristic path length (CPL, P = 0.056), significant global
increases in normalized CPL (1.27 – 0.02 vs 1.35 – 0.03), decreases in
network efficiency (1.32e - 2 – 2.3e -4 vs 1.26e - 2 – 1.89e - 4) but no
difference in the clustering coefficient (all two-tailed t-tests, P < 0.05).
One potential explanation for this is reduced long-range connections.
As expected, measures of local connectivity were largely in agreement
with the TBSS data ipsilaterally, with reductions in network strength,
betweenness_centrality, clustering_coefficient and regional and local
efficiency (P < 0.05, one-tailed FDR-corrected). However, unlike the
TBSS data, there were also notable reductions in many of these
measures within contralateral regions (M2, S1, Cg1/2), bilaterally in
the PF-cortex, as well as the fimbria, posterior RSG-cortex and the
hypothalamus suggesting much wider decreases in anatomical con-
nectivity. More unexpectedly, when we re-ran the analysis using the
more stringent two-tailed-t-test, in addition to most of the prior net-
work deficits, we found significant increases in ‘‘hubness’’ and
strength of connectivity bilaterally in M1 cortex and thalamus, im-
plying potential spontaneous reorganization at the structural level.
Partial agreement from our functional connectivity data (see accom-
panying abstract) would appear to support this conclusion. Support:
UCLA_BIRC.
Key words
connectivity, DTI
A2-12
TEMPORAL ALTERATIONS IN FUNCTIONAL CON-
NECTIVITY AFTER EXPERIMENTAL TRAUMATIC BRAIN
INJURY
Harris, N.G., Verley, D.R., Yeh, H.J.
University of California, Los Angeles, USA
Spontaneous resolution of sensory-motor behavioral deficits following
TBI is a well-known phenomenon that occurs both after experimental
and clinical TBI. Our prior functional MRI (fMRI) data has shown
that reorganization of brain circuits is an important component of this.
However, use of evoked fMRI to study cortical map plasticity only
allows one circuit to be studied so that a limited snapshot of circuit
reorganization is permitted. On the other hand, resting state fMRI
(rsFMRI) allows an unbiased view of brain functional connectivity
(fc) across multiple brain networks so that it might provide a useful
approach to understanding brain functional reorganization after injury.
We therefore acquired rsFMRI data before, and at weekly intervals
until 4-weeks after unilateral CCI injury over the forelimb sensori-
motor cortex in adult, male rats (n = 9). Using group-wise independent
component analysis (ICA) to identify the major networks and with
verification using seed-based correlation analysis, we found that un-
like many of the bilaterally present cortical and subcortical networks
observable before injury, the number of cortical networks were re-
duced ipsi-lesionally at 7-days after injury and those present were
enlarged (voxel-based analysis, P < 0.05), suggesting reduced intra-
hemispheric and increased intra-cortical fc, in agreement with our
prior structural fc data in this model. Despite the confinement of
primary injury to cortical areas, caudate fc was significantly reduced
ipsi-lesionally at 7-days and this persisted through 4-weeks post-
injury indicating more widespread dysfunction than previously seen
(P < 0.05). Between 7 and 28 days there was an ipsi-to-contra-lesional
shift in the cortical components so that only 1 minor, ipsi-lesional
anterior motor network remained, while the contra-lesional cortex
components were more numerous and similar to pre-injury. We also
used graph theory methods to quantify network-level disturbances in
more detail using anatomically-defined nodes from a co-registered,
segmented brain atlas. Results were largely in agreement with the
ICA analysis with regard to decreased connectivity, but in addi-
tion, increased local connectedness across novel nodes was ap-
parent at 28 days within the ipsi-lesional hemisphere. Support:
UCLA BIRC
Key words
connectivity, connectomics, resting state fMRI
A2-13
RECRUITMENT, SCREENING, AND CLASSIFICATION OF
ACUTE TBI: ADVANTAGES OF A MULTI-PATHWAY
SCREENING PROTOCOL
Afzal, M.M.1, Latour, L.L.1,2, Armstrong, R.C.1,3, Butman, J.A.1,4, Chan,
L.1,4, Cota, M.R.1, Dsurney, J.1, Eisenberg, H.M.5, Fitzsimmons, S.M.1,
A-28