Publications by authors named "Isaac Pedisich"

4 Publications

  • Page 1 of 1

Closed-loop stimulation of temporal cortex rescues functional networks and improves memory.

Nat Commun 2018 02 6;9(1):365. Epub 2018 Feb 6.

Department of Psychology, University of Pennsylvania, 433 South University Avenue, Philadelphia, PA, 19104, USA.

Memory failures are frustrating and often the result of ineffective encoding. One approach to improving memory outcomes is through direct modulation of brain activity with electrical stimulation. Previous efforts, however, have reported inconsistent effects when using open-loop stimulation and often target the hippocampus and medial temporal lobes. Here we use a closed-loop system to monitor and decode neural activity from direct brain recordings in humans. We apply targeted stimulation to lateral temporal cortex and report that this stimulation rescues periods of poor memory encoding. This system also improves later recall, revealing that the lateral temporal cortex is a reliable target for memory enhancement. Taken together, our results suggest that such systems may provide a therapeutic approach for treating memory dysfunction.
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http://dx.doi.org/10.1038/s41467-017-02753-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5802791PMC
February 2018

Proximity of Substantia Nigra Microstimulation to Putative GABAergic Neurons Predicts Modulation of Human Reinforcement Learning.

Front Hum Neurosci 2017 9;11:200. Epub 2017 May 9.

Department of Psychology, University of PennsylvaniaPhiladelphia, PA, USA.

Neuronal firing in the substantia nigra (SN) immediately following reward is thought to play a crucial role in human reinforcement learning. As in Ramayya et al. (2014a) we applied microstimulation in the SN of patients undergoing deep brain stimulation (DBS) for the treatment of Parkinson's disease as they engaged in a two-alternative reinforcement learning task. We obtained microelectrode recordings to assess the proximity of the electrode tip to putative dopaminergic and GABAergic SN neurons and applied stimulation to assess the functional importance of these neuronal populations for learning. We found that the proximity of SN microstimulation to putative GABAergic neurons predicted the degree of stimulation-related changes in learning. These results extend previous work by supporting a specific role for SN GABA firing in reinforcement learning. Stimulation near these neurons appears to dampen the reinforcing effect of rewarding stimuli.
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http://dx.doi.org/10.3389/fnhum.2017.00200DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5422436PMC
May 2017

Direct Brain Stimulation Modulates Encoding States and Memory Performance in Humans.

Curr Biol 2017 May 20;27(9):1251-1258. Epub 2017 Apr 20.

Department of Psychology, University of Pennsylvania, Philadelphia, PA 19104, USA. Electronic address:

People often forget information because they fail to effectively encode it. Here, we test the hypothesis that targeted electrical stimulation can modulate neural encoding states and subsequent memory outcomes. Using recordings from neurosurgical epilepsy patients with intracranially implanted electrodes, we trained multivariate classifiers to discriminate spectral activity during learning that predicted remembering from forgetting, then decoded neural activity in later sessions in which we applied stimulation during learning. Stimulation increased encoding-state estimates and recall if delivered when the classifier indicated low encoding efficiency but had the reverse effect if stimulation was delivered when the classifier indicated high encoding efficiency. Higher encoding-state estimates from stimulation were associated with greater evidence of neural activity linked to contextual memory encoding. In identifying the conditions under which stimulation modulates memory, the data suggest strategies for therapeutically treating memory dysfunction.
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http://dx.doi.org/10.1016/j.cub.2017.03.028DOI Listing
May 2017

Expectation modulates neural representations of valence throughout the human brain.

Neuroimage 2015 Jul 30;115:214-23. Epub 2015 Apr 30.

Department of Psychology, University of Pennsylvania, Philadelphia, PA 19104, USA. Electronic address:

The brain's sensitivity to unexpected gains or losses plays an important role in our ability to learn new behaviors (Rescorla and Wagner, 1972; Sutton and Barto, 1990). Recent work suggests that gains and losses are ubiquitously encoded throughout the human brain (Vickery et al., 2011), however, the extent to which reward expectation modulates these valence representations is not known. To address this question, we analyzed recordings from 4306 intracranially implanted electrodes in 39 neurosurgical patients as they performed a two-alternative probability learning task. Using high-frequency activity (HFA, 70-200 Hz) as an indicator of local firing rates, we found that expectation modulated reward-related neural activity in widespread brain regions, including regions that receive sparse inputs from midbrain dopaminergic neurons. The strength of unexpected gain signals predicted subjects' abilities to encode stimulus-reward associations. Thus, neural signals that are functionally related to learning are widely distributed throughout the human brain.
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http://dx.doi.org/10.1016/j.neuroimage.2015.04.037DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4550220PMC
July 2015