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Magnitude of task-induced deactivation of insula and anterior cingulate cortex is related to inter-individual differences in RMSSD

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By combining functional Magnetic Resonance Imaging and acquisition of cardiac pulsation during the execution of a cognitive task we identified areas where task-induced changes in brain activity correlated with individuals' cardiac RMSSD. We show the existence of a relationship between task - induced deactivations and RMSSD.
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Abstract By combining functional Magnetic Resonance
Imaging and acquisition of cardiac pulsation during the
execution of a cognitive task we identified areas where task-
induced changes in brain activity correlated with individuals'
cardiac RMSSD. We show the existence of a relationship
between task - induced deactivations and RMSSD.
I. INTRODUCTION
The relation between brain function, as measured by
noninvasive functional Magnetic Resonance Imaging (fMRI)
and physiological fluctuations is one of the most debated
topics in the last decade [1]. We used fMRI and an inter-
individual differences analysis to identify brain regions
where the magnitude of task-induced changes in brain
activity correlated with individuals’ RMSSD during task
performance (brain/behavior correlations). We then
determined whether these regions showed task-induced
activation or deactivation. We found that brain regions
demonstrating brain/behavior correlations, notably including
the insula and anterior cingulate cortex, tended to be task-
deactivated. Thus, the magnitude of deactivation in task-
deactive regions partially reflects modulation of autonomic
nervous system activity.
II. METHODS
Participants: 11 participants (7 males, mean age = 24.6
yrs, std = 3.5) took part in the study. Brain imaging
acquisitions: 1 structural (MPRAGE) image was acquired
(spatial resolution = 1 mm isotropic, 176 sagittal slices). One
fMRI scan was acquired as well (115 scans / 253 sec,
temporal resolution = 2.2 sec, spatial resolution = 3x3x3
mm, 0.45 mm slice spacing, 37 axial, parallel to AC - PC
slices). During the fMRI session, participants engaged in a
mental arithmetic Continuous Performance Task (CPT),
which had a 4-cycle on/off structure (ABABABAB), where
A = 10 sec rest period; B = 30 sec task period (B).
Cardiac data were recorded during the CPT using a
photoplethysmograph placed on participants’ left forefinger
(sampling frequency = 50 Hz). Cardiac data were evaluated
manually and annotated to reflect correct R-R intervals. To
define an autonomic index we first established the inter-beat
interval (IBI) series in the task performance block (initial
30sec task block) and from the IBI series we derived a series
reflecting the root mean square of subsequent differences
(RMSSD, [2]) of the IBIs. This resulted in a single
autonomic activity indicant for each participant. RMSSD
Research supported by European Research Council (ERC) starting grant,
NeuroInt to U. H
V.Iacovella is with Fondazione Bruno Kessler, Italy (*corresponding
author e-mail: iacovella@fbk.eu).
Uri Hasson is with the Center For Mind and Brain Sciences, The
University of Trento, Italy
indexes beat-to-beat variation and reflects a mainly vagal
HRV component.
Neuroimaging analysis consisted of constructing two
statistical parametric maps (SPMs) reflecting features of
brain activity, and then relating the two maps. One SPM
indicated task-related changes in brain activity. The other
SPM was based on inter-individual differences, and identified
brain regions where the magnitude of task-related activation
correlated with participants RMSSD values.
1. Modeling: For each voxel (the 3mm
3
fMRI spatial
sampling unit), activation was defined as the correlation
between the timeline of the study (i.e., the 30sec on / 10
seconds off cycle) and the voxel’s time series. This was done
via a regression model: Voxel
timeseries
= β * study_timeline + ε.
Here β is the regression slope.
2. Group level activation SPM: After obtaining the
voxel’s β in step #1 for each participant, a voxel-wise one-
sample T-test evaluated whether the mean β for the voxel,
across participants, departed from chance; i.e., 0 (statistical
significance set at p < .005, T
(10)
> 2.71). Family-Wise Error
(FWE) control for multiple comparisons was implemented
via cluster-wise thresholding [3], which identifies contiguous
clusters of statistically significant voxels (FWE p < .05 using
cluster extent). This defined, on a group-level, task-activated
or task-deactivated clusters (see Fig. 1A), and constitutes a
validity check for the study, as its results should replicate
prior paradigms.
3. Group level correlation SPM: For each voxel, we
calculated the correlation (Pearson’s R) between participants’
β values and their RMSSD during task performance
(β:RMSSD correlation henceforth). FWE was implemented
as described above (single voxel p < .005 uncorrected; FWE
controlled using cluster extent, p < .05). This identified
clusters where all voxels showed a significant β:RMSSD
correlation (see Fig. 1B).
4. Finally, we treated each cluster in which the
β:RMSSD correlation was significant (step #3) as a
functional ‘region of interest’. For each region we determined
if it was associated with task-related activation or
deactivation, by calculating the mean β in the cluster per
participant, and conducting a T-test against 0. This indicated
which of the clusters that showed β:RMSSD correlations
were also significantly task-activated or deactivated. This
analysis returns a matrix that partitions clusters with
β:RMSSD correlations into four types depending on whether
the correlation was positive/negative and whether voxels in
these clusters tended to be task-active or task-deactive (Fig.
1C).
Magnitude of Task-induced Deactivation of Insula and Anterior
Cingulate Cortex is related to Inter-individual Differences in
RMSSD
Vittorio Iacovella*, Uri Hasson
I. RESULTS AND CONCLUSIONS
Task related effects: task execution resulted in both task-
induced activation and task-induced deactivation (Fig. 1A,
warm and cool tones respectively). The distribution of
deactive regions very well matched a cortical network termed
the ‘default mode network’, thought to mediate intrinsic
awareness and mind wandering [4]. Active areas matched
prior reports of mental arithmetic [5], including areas
involved in attention and verbal rehearsal (e.g., left inferior
frontal gyrus).
Correlation with RMSSD: areas showing a correlation
between task-induced effects and RMSSD included ones with
either positive (Fig. 1B, warm tones) or negative (Fig. 1B,
cool tones) correlations. Areas showing positive relations
included motor cortex, STG, ACC, PCC and ant. Insula (see
Fig. 1 for acronyms). Areas showing negative correlations
included the anterior superior insula and calcarine sulcus. The
results corroborate the insula’s involvement in autonomic
processes [6], and its functional segregation into 3 areas [7]:
posterior, anterior inferior and anterior superior, where the
latter show a different relationship between task - related
effects and autonomic activity indicant. We note that
participants’ RMSSD measures collected during rest did not
correlate with RMSSD during task execution, suggesting
phasic task effects.
Cross-referencing the task-related and autonomic effects
(Fig. 1A, 1B) classified areas as function of the sign of
correlation with RMSSD (positive/negative) and whether
they were task-active or task-deactive. Of the 38 clusters
showing β:RMSSD correlations, 1 was significantly task-
active, 11 were significantly task-deactive, and 22 did not fall
into either category. Fig. 1C characterizes these clusters via a
matrix: each point corresponds to a cluster extracted from the
β:RMSSD SPM, which was task-active or task-deactive. The
ordinate marks the mean β:RMSSD correlation in the cluster,
and the abscissa marks whether the mean β in the cluster
indicated task-induced activation or deactivation. The modal
pattern in the identified clusters was one associated with
positive β:RMSSD correlations, but task related deactivation,
which notably held for the posterior and anterior left inferior
insula, PCC, ACC and ITG. One area, the calcarine sulcus,
was an exception to this pattern, showing task-related
activation and a negative β:RMSSD correlation.
Our findings show that inter-individual differences in
RMSSD are linked to the degree of task-related deactivation
of areas frequently associated with the regulation or
monitoring of autonomic activity, including insula and ACC.
Greater task-related deactivation was associated with lower
RMSSD. This suggests that task execution might shape
information processing in deactive areas: even if they are not
directly involved in accomplishing external requests, they
might be in charge of relating with vagal fluctuations and
maintain basic internal autonomic functions.
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Fig. 1. (A) Areas where performance of a mental arithmetic task caused
task-related activation (warm tones) or deactivation (blue tones). (B) Areas
where inter-individual differences in task-induced activity correlated with
differences in RMSSD. (C) Characterization of clusters based on correlation
and activation patterns (see text). Most of the areas (top left box) show task
related-deactivation, and a positive correlation between activity values and
RMSSD. “l” = left; “r” right; “a” = anterior; “p” = posterior; ACC/PCC =
anterior/posterior cingulate cortex; ITG/STG = inferior/superior temporal
gyrus; SFG = superior frontal gyrus; CaG = Calcarine gyrus.
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