Low Intensity Focused Ultrasound for Learning and Memory (LIFUPMEM)

Low Intensity Focused Ultrasound of Medial Temporal Lobe Regions for the Improvement of Learning and Memory

Hippocampus and medial temporal lobe (MTL)-dependent memory is impacted by a wide range of psychiatric and neurologic conditions. These cognitive limitations often result in limited functional abilities for patients. Currently available pharmacologic and behavioral treatments are somewhat controversial and have minimal evidence-based effectiveness. Recently, deep brain stimulation was used to modulate MTL activity and subsequently improve memory performance. However, such implantable devices require neurosurgery with major associated health risk. At present, there are no publications reporting non-invasive neurostimulation targeting MTL regions to improve memory. The central hypothesis of this project is that non-invasive, low intensity focused ultrasound pulsation (LIFUP) can selectively increase regional MTL activity and thus be used as a cognitive neural prosthetic capable of improving memory performance. The aims of this study focus on whether LIFUP can increased blood oxygen level dependent (BOLD) activation in the entorhinal cortex and functionally associated regions, whether this increased activation is greater using short train or long train LIFUP parameters, and whether this LIFUP-induced activation, when applied during learning, results in improved memory.

This proposal proposes the use of personalized neuronavigation, based on each participant's structural brain MRI, to aim LIFUP at the white matter underlying the entorhinal cortex in the pursuit of enhancement of learning and memory in humans. A comprehensive approach will integrate behavioral and multimodal neuroimaging to assess the utility of LIFUP to increase activity in deep neural structures and in the enhancement of memory. Further, this is the first study to use LIFUP in (A) ventral cortical and hippocampal regions and (B) for pro-cognitive effects. Findings from this study will provide important insight into the utility of LIFUP modulation of subcortical regions and their associated networks and functions, which have wide ranging implications for clinical LIFUP as a therapeutic device for numerous patient populations. Participants will complete a brief T1-weighted structural brain scan. Then, they will be removed from the scanner and, using the T1 image in Neurocare Brainsight software60, the LIFUP transducer will be aimed at the white matter underlying the entorhinal cortex and gently strapped in place to their head. Participants will then return to the scanner where a second T1 image will verify the position of the LIFUP transducer and allow for estimation of the spatial location of the sonification beam focus (approximately .5cm long x 7mm diameter). BOLD fMRI will be collected during three conditions, randomized and counterbalanced across participants (with sham always separating the two LIFUP conditions: short train sonification LIFUP, sham LIFUP long train LIFUP: total time = 30min. Short train LIFUP (previously used in primary sensory cortices47 will be administered in 75 sonifications at 210 KHz frequency with pulse repetition frequency of 500Hz, 35mW/cm2, sonification duration 0.5s with 7s inter-stimulation interval. Sham LIFUP will involve the same procedures (e.g. participant provided the same instructions) except the sonification will not occur. Before and after completing the scan and a short break, these participants will receive short train LIFUP47 while they are administered a series of three computerized, hippocampally-dependent episodic memory tasks. Given that routine clinical neuropsychological measures are designed to provide diagnostic information and are not sensitive or specific enough to precisely measure longitudinal cognitive change related to an intervention, we will use validated experimental neurocognitive measures.

Participants will be blinded to whether or not the LIFUP transducer is on and, when on, what parameters are used. The investigator collecting the neuropsychological data will be blinded to which condition (LIFUP, sham) the participant completed during the session. The statistical analysts for both the neuropsychological and neuroimaging data will also be blinded to condition.

Low Intensity focused ultrasound pulsation will be administered to participants while they are in the fMRI scanner. Functional and perfusion MR data will be collected before and after the sonication to allow for comparisons and investigation of pre and post sonication functional activation and connectivity.

While in the fMRI scanner, participants will have the ultrasound transducer attached to their head in the same manner as during the actual ultrasound sonication. However, during this portion of the experiment, the transducer will not be turned on. Previous, published experiments indicate that participants are unable to differentiate between when the transducer is on and off.

BOLD fMRI will be collected during two conditions (given that the timecourse of LIFUP related changes is unknown, sham will always precede the LIFUP condition). LIFUP (previously used in primary sensory cortices will be administered in 75 sonifications at 210 KHz frequency with pulse repetition frequency of 500Hz, 35mW/cm2, sonification duration 0.5s with 7s inter-stimulation intervals. Sham LIFUP will involve the same procedures (e.g. participant provided the same instructions) except the sonification will not occur.

BOLD fMRI will be collected while the ultrasound trandsducer is not turned on. Participants are unable to tell whether the transducer is on or off.

Number of words learned across each learning trial and number of words recalled during the delayed recall trial will be compared before and after sonication for each participant in a within subject design.

BOLD data will be collected in real-time during the ultrasound sonication, which occurs in on-off blocks. Analyses will assess the statistical relationship between BOLD signal in the brain and the time series (on vs off) of the ultrasound sonication.

Perfusion ASL fMRI data will be collected before and after sonication. Analyses will assess the statistical relationship between ASL signal throughout the brain pre and post sonication in a within subject repeated measures design.

Inclusion Criteria: Must be between 35-65 years of age Must be right handed English must be the dominant language Exclusion Criteria: contraindications for MRI (e.g. metal implants, pregnancy) history of head injury sufficient to warrant medical attention history of alcohol abuse or dependence history of substance abuse or dependence history of major psychiatric illness requiring treatment history of cancer or other neoplastic syndromes history of major neurologic illness (e.g. epilepsy).