Task-dependent activity and connectivity predict episodic memory network-based responses to brain stimulation in healthy aging.
BACKGROUND
Transcranial magnetic stimulation (TMS) can affect episodic memory, one of the main cognitive hallmarks of aging, but the mechanisms of action remain unclear.


OBJECTIVE
To evaluate the behavioral and functional impact of excitatory TMS in a group of healthy elders.


METHODS
We applied a paradigm of repetitive TMS - intermittent theta-burst stimulation - over left inferior frontal gyrus in healthy elders (n = 24) and evaluated its impact on the performance of an episodic memory task with two levels of processing and the associated brain activity as captured by a pre and post fMRI scans.


RESULTS
In the post-TMS fMRI we found TMS-related activity increases in left prefrontal and cerebellum-occipital areas specifically during deep encoding but not during shallow encoding or at rest. Furthermore, we found a task-dependent change in connectivity during the encoding task between cerebellum-occipital areas and the TMS-targeted left inferior frontal region. This connectivity change correlated with the TMS effects over brain networks.


CONCLUSIONS
The results suggest that the aged brain responds to brain stimulation in a state-dependent manner as engaged by different tasks components and that TMS effect is related to inter-individual connectivity changes measures. These findings reveal fundamental insights into brain network dynamics in aging and the capacity to probe them with combined behavioral and stimulation approaches.
Department de Psiquiatria i Psicobiologia Clinica, Universitat de Barcelona, Barcelona, Spain.
Dídac
D
Vidal-Piñeiro
Department de Psiquiatria i Psicobiologia Clinica, Universitat de Barcelona, Barcelona, Spain.
Pablo
P
Martin-Trias
Department de Psiquiatria i Psicobiologia Clinica, Universitat de Barcelona, Barcelona, Spain.
Eider M
EM
Arenaza-Urquijo
Department de Psiquiatria i Psicobiologia Clinica, Universitat de Barcelona, Barcelona, Spain.
Roser
R
Sala-Llonch
Department de Psiquiatria i Psicobiologia Clinica, Universitat de Barcelona, Barcelona, Spain; Institute for Brain, Cognition and Behaviour (IR3C), Barcelona, Spain.
Imma C
IC
Clemente
Department de Psiquiatria i Psicobiologia Clinica, Universitat de Barcelona, Barcelona, Spain.
Isaias
I
Mena-Sánchez
Institut d'Investigacions Biomèdiques August Pi i Sunyer, Barcelona, Spain; Secció de Neuroradiologia, Servei de Radiologia, Centre de Diagnòstic per la Imatge, Barcelona, Spain.
Núria
N
Bargalló
Institut d'Investigacions Biomèdiques August Pi i Sunyer, Barcelona, Spain; CIBER-BBN, Barcelona, Spain.
Carles
C
Falcón
Berenson-Allen Center for Noninvasive Brain Stimulation, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, USA; Institut Universitari de Neurorehabilitació Guttmann-UAB, Badalona, Spain.
Álvaro
Á
Pascual-Leone
Department de Psiquiatria i Psicobiologia Clinica, Universitat de Barcelona, Barcelona, Spain; Institut d'Investigacions Biomèdiques August Pi i Sunyer, Barcelona, Spain. Electronic address: dbartres@ub.edu.
David
D
Bartrés-Faz
D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D001921:Brain / Q000502:physiology*; D001931:Brain Mapping; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D061212:Memory, Episodic; D008875:Middle Aged; D009415:Nerve Net / Q000502:physiology*; D009483:Neuropsychological Tests; D050781:Transcranial Magnetic Stimulation / Q000379:methods*
Aging; Episodic memory; Functional magnetic resonance imaging; Level of processing; Transcranial magnetic stimulation