Variability of scaling exponents in short-term memory fMRI time series
Presenting author:
Functional activations have a non-trivial auto-correlation and cross-correlation structure. Here, we studied diurnal variation of working memory distortions [1,2] in four types of experimental tasks: two visual-verbal (V; semantically or phonetically associated words) and two non-verbal (NV; pictures of similar objects). The regional activity was quantified with the Hurst exponent (H), detrended fluctuation analysis [3] and detrended cross-correlation coefficients [4].
The signals in specific occipital lobe areas depend not only on the type of experimental tasks but also on information memorisation or retrieval. A particularly apparent difference is visible between memorisation in V and NV tasks. In the former, for some brain regions in the Visual II resting-state (RS) network, the H exponents are very close to 0.5, indicating a lack of linear temporal correlations [5]. In the latter, we observe persistent behaviour. The reduction of H in tasks relative to RS is significant in many brain areas.
We additionally uncovered regionally coordinated changes by comparing distributions of appropriately clustered eigenvalues of cross-correlation matrices. The detrended correlations were more sensitive than linear ones, showing the greatest differences between: RS and other tasks, memorisation and retrieval, V and NV tasks.
References
1. Atkins, A.S., Reuter-Lorenz, P.A. NeuroImage 56, 1726–1734 (2011)
2. Lewandowska, K., et al. Chronobiology International 35(1), 80–89 (2018)
3. Kantelhardt, J.W. et al. Physica A: Statistical Mechanics and its Applications 316, 87–114 (2002)
4. Kwapień, J., Oświęcimka, P., Drożdż, S. Physical Review E 92, 052815(2015)
5. Oświęcimka, P., Kwapień, J., Drożdż, S. Physical Review E 74, 016103 (2006)
The signals in specific occipital lobe areas depend not only on the type of experimental tasks but also on information memorisation or retrieval. A particularly apparent difference is visible between memorisation in V and NV tasks. In the former, for some brain regions in the Visual II resting-state (RS) network, the H exponents are very close to 0.5, indicating a lack of linear temporal correlations [5]. In the latter, we observe persistent behaviour. The reduction of H in tasks relative to RS is significant in many brain areas.
We additionally uncovered regionally coordinated changes by comparing distributions of appropriately clustered eigenvalues of cross-correlation matrices. The detrended correlations were more sensitive than linear ones, showing the greatest differences between: RS and other tasks, memorisation and retrieval, V and NV tasks.
References
1. Atkins, A.S., Reuter-Lorenz, P.A. NeuroImage 56, 1726–1734 (2011)
2. Lewandowska, K., et al. Chronobiology International 35(1), 80–89 (2018)
3. Kantelhardt, J.W. et al. Physica A: Statistical Mechanics and its Applications 316, 87–114 (2002)
4. Kwapień, J., Oświęcimka, P., Drożdż, S. Physical Review E 92, 052815(2015)
5. Oświęcimka, P., Kwapień, J., Drożdż, S. Physical Review E 74, 016103 (2006)