Resting State Functional Connectivity of the Hippocampus in the
Context of Emotional and Neutral Stimuli
Neuroimaging
Laboratory
Kellie McWilliams, Julie Petersen, J. Michael Williams, PhD,
& Karol Osipowicz, PhD
Department of Psychology, Drexel University
Past studies have shown that stimulation of the limbic system,
particularly of the amygdala, in response to emotion stimuli
increases the connectivity between the limbic system and the
hippocampus, thereby enhancing the functioning of the
hippocampus and creating a more stable memory trace [2]. This
interaction occurs simultaneously with the flow of information from
cortical sensory systems into the medial temporal lobes, placing
the hippocampus in a unique position to act as a binding site,
coupling emotional tone with sensory content [3]. After encoding
newly stabilized memory traces are sent from the hippocampus
back out to cortical regions for storage through the process of
consolidation [4]. This model views the hippocampus as a “pass
through” structure, responsible for associating various memory
components to form a meaningful memory trace. Therefore, we
hypothesize that the hippocampus will show extensive
connectivity to the both the cortical sensory systems and limbic
system.
Primary Results
Secondary Results
ROI resting state analysis between the hippocampus and limbic
and cortical sensory systems revealed extensive connectivity of
the left and right hippocampus to both systems (figures 1-3).
Additionally, a limbic specific network reflecting just the emotional
component of encoding was identified (figure 4).
Fig. 4 Correlation with recognition scores (emotional greater than
neutral)
Fig. 1 Hippocampal connectivity to all systems
Left Hippocampus
Right Hippocampus
Methods
Twenty one healthy, normal adults (10 males) participated (Mage =
25 yrs, SDage = 4). After screening for neurological, psychiatric,
and psychological disorders and for contraindications to MRI,
participants were scanned using a 3.0 T scanner. Participants
were presented with and asked to memorize emotional and
neutral stimuli, including pictures, words, and environmental
sounds. After presentation of the stimuli, resting state data was
collected. Memory for the stimuli was assessed following the
scanning. Participants were scored on recognition of stimuli. Data
was analyzed using SPM and CONN software.
Analysis
Data preprocessing included slice time correction, realignment,
coregistration (MNI), normalization (MNI), and smoothing (5mm).
Functional connectivity analyses focused on Amplitude of Low
Frequency Fluctuations (ALFF) measures of the amplitude of
regional activity and intra- and inter-regional time series
similarities. The data was analyzed in CONN using the posterior
hippocampus as a seed region (as defined by fMRI analysis). An
additional analysis contrasting recognized emotional stimuli with
recognized neutral stimuli was also run.
Conclusions
Fig. 2 Hippocampal connectivity to cortical sensory systems
Fig. 3 Hippocampal connectivity to the limbic system
An extensive number of functional connections was observed
between the hippocampus and the limbic and cortical sensory
systems. This puts the hippocampus in an ideal position to act as
an interface between the cortical sensory systems and the limbic
system. The hippocampus has the unique ability to receive
information from both systems and combine them in a meaningful
way before passing the now associated memory components
back to cortex for storage. We also identified a network
contributing to the emotional component of memory encoding by
contrasting emotional stimuli recognition with stimuli recognition in
general. The existence of this network supports the theory that
emotion modulates hippocampal function and memory encoding
through the connectivity of the limbic system to the hippocampus.
References:
1.Smith, A.P.R., et al., Task and Content Modulate Amygdala-Hippocampal Connectivity in Emotional Retrieval. Neuron, 2006.
49(4): p. 631-638.
2.Phelps, E.A., Human emotion and memory: interactions of the amygdala and hippocampal complex. Current opinion in
neurobiology, 2004. 14(2): p. 198-202.
3.Cohen, N.J., et al., Hippocampal system and declarative (relational) memory: Summarizing the data from functional
neuroimaging studies. Hippocampus, 1999. 9(1): p. 83-98.
4.Nadel, L., et al., Memory formation, consolidation and transformation. Neuroscience & Biobehavioral Reviews, 2012. 36(7):
p. 1640-1645.