We will determine the utility of a novel brain mapping technique for epilepsy presurgical
evaluation, referred to as 'six-dimensional (6D) dynamic tractography'. This innovative
program animates the rapid neural propagations along MRI-defined, 3D white matter tracts
that connect regions supporting cognitive functions. Specifically, it will use
event-related high gamma activity to localize the regions supporting specific linguistic
functions and compute the velocity and strength of neural propagations based on the
latency and amplitude of early neural responses to single-pulse electrical stimulation.
We expect that considering both the negative effect of damaged white matter tracts and
the positive effect of seizure control will help optimize the model's performance in
predicting postoperative language outcomes; this will be accomplished by incorporating
the 6D dynamic tractography and objective epilepsy biomarkers, including spontaneous
high-frequency oscillations (HFOs) coupled to slow-waves, into our predictive model. By
also identifying and considering the physiological high gamma augmentation strictly
time-locked to stimuli and behaviors, our innovative intracranial EEG analysis will
better distinguish the randomly-occurring pathologic HFOs. Another significant
advancement provided by our model is its independence of conventional electrical
stimulation mapping, which can acutely elicit seizures and fail to satisfactorily
localize language areas in certain patient subsets. Additionally, this project will use
6D dynamic tractography to provide an explicit neurobiological model of language network
dynamics, allowing us to tease apart the specific pathways originating from temporal lobe
cortices that support the lexical retrieval of auditory or visual domains. Our prior
project indicated that the arcuate fasciculus fibers support the direct transfer of
lexical representations of auditory sentences. We will now determine whether the lexical
representations of visual objects are likewise transferred via the arcuate fasciculus or
others, including the fusiform-parietal fasciculus. To accomplish these goals, this
project will prospectively recruit a new cohort of 80 epilepsy patients - age range: 0.5
to 21 years - undergoing extraoperative intracranial EEG recording and subsequent
resective surgery. Finally, we will determine if the human brain creates and strengthens
language-related functional parcellations throughout development. It has been suggested
that the adult brain efficiently activates the posterior superior-temporal gyrus (STG)
only during sound onset to decode the boundary between sounds. In contrast, the anterior
STG shows sustained activation during an auditory stimulus to encode the phonetic
features. We will determine if such a functional parcellation is more evident in older
individuals, whose brains are more developed. While providing hypotheses focusing on
specific brain regions, we will perform all of the proposed analyses at the whole-brain
level. We will make all data and codes publicly available to facilitate external
validation and implementation.
