Samantha Gray

All Publications

• Episodic memory involves transient and sparse connectivity aligned to both internal and external events. PLoS biology Dede, A. J., Cross, Z. R., Gray, S. M., Kelly, J. P., Yin, Q., Vahidi, P., Asano, E., Schuele, S. U., Rosenow, J. M., Wu, J. Y., Lam, S. K., Raskin, J. S., Lin, J. J., Kim McManus, O., Sattar, S., Shaikhouni, A., King-Stephens, D., Weber, P. B., Laxer, K. D., Brunner, P., Roland, J. L., Saez, I., Girgis, F., Knight, R. T., Ofen, N., Johnson, E. L. 2025; 23 (11): e3003481

  Abstract

  Episodic memory depends on the coordination of local processing, indexed by high-frequency broadband (HFB) activity, with global organization, indexed by theta oscillations. However, theta and HFB exhibit asynchronous timing, raising the question of how results of local processing are communicated. Using intracranial EEG in patients performing a recognition memory task, we examined this coordination across medial temporal (MTL) and prefrontal (PFC) regions. HFB peaks occurred earlier in the MTL than in the PFC. Contrasting analyses were anchored either to these internally driven HFB peaks or to the external event of stimulus presentation. We discovered three key results. First, the role of the PFC changed from encoding to retrieval. Specifically, PFC-MTL theta connectivity was aligned with internal PFC peaks during encoding, suggesting top-down initiation. By contrast, this connection was aligned with external stimulus presentation during retrieval, suggesting bottom-up initiation. Second, the anterior cingulate cortex exhibited connectivity that was aligned to internal HFB peaks only, suggesting that its role is evaluative, devoid of direct stimulus processing. Third, graph theoretic analysis of whole-brain connectivity patterns revealed that the connections predicting successful memory performance were embedded in transient, sparse network states. These results reveal that analyses triggered from internally-generated events yield different results when compared to classic analyses triggered using external events. The picture that emerges is a sequence of specific, short-lived, internally-generated states that drive episodic memory success.

  View details for DOI 10.1371/journal.pbio.3003481

  View details for PubMedID 41289341

• The development of aperiodic neural activity in the human brain. Nature human behaviour Cross, Z. R., Gray, S. M., Dede, A. J., Rivera, Y. M., Yin, Q., Vahidi, P., Rau, E. M., Cyr, C., Holubecki, A. M., Asano, E., Lin, J. J., Kim McManus, O., Sattar, S., Saez, I., Girgis, F., King-Stephens, D., Weber, P. B., Laxer, K. D., Schuele, S. U., Rosenow, J. M., Wu, J. Y., Lam, S. K., Raskin, J. S., Chang, E. F., Shaikhouni, A., Brunner, P., Roland, J. L., Braga, R. M., Knight, R. T., Ofen, N., Johnson, E. L. 2025

  Abstract

  The neurophysiological mechanisms supporting brain maturation are fundamental to attention and memory capacity across the lifespan. Human brain regions develop at different rates, with many regions developing into the third and fourth decades of life. Here, in this preregistered study ( https://osf.io/gsru7 ), we analysed intracranial electroencephalography recordings from widespread brain regions in a large developmental cohort. Using task-based (that is, attention to to-be-remembered visual stimuli) and task-free (resting-state) data from 101 children and adults (5.93-54.00 years, 63 males; n electrodes = 5,691), we mapped aperiodic (1/ƒ-like) activity, a proxy of neural noise, where steeper slopes indicate less noise and flatter slopes indicate more noise. We reveal that aperiodic slopes flatten with age into young adulthood in both association and sensorimotor cortices, challenging models of early sensorimotor development based on brain structure. In the prefrontal cortex (PFC), attentional state modulated age effects, revealing steeper task-based than task-free slopes in adults and the opposite in children, consistent with the development of cognitive control. Age-related differences in task-based slopes also explained age-related gains in memory performance, linking the development of PFC cognitive control to the development of memory. Last, with additional structural imaging measures, we reveal that age-related differences in grey matter volume are similarly associated with aperiodic slopes in association and sensorimotor cortices. Our findings establish developmental trajectories of aperiodic activity in localized brain regions and illuminate the development of PFC control during adolescence in the development of attention and memory.

  View details for DOI 10.1038/s41562-025-02270-x

  View details for PubMedID 40670699

  View details for PubMedCentralID 9021021