title: Heterogeneity of stimulus-specific response modification-an fMRI study on neuroplasticity.
abstract: Long-term potentiation (LTP) is a key element of synaptic plasticity. At the macroscopic level, similar effects can be induced in the human brain using repetitive stimulation with identical stimuli. High-frequency stimulation (HFS) can increase neuronal responses whereas low-frequency stimulation may produce the opposite effect. Optimal stimulation frequencies and characteristics for inducing stimulus-specific response modification (SRM) differ substantially from those applied to brain tissue slices but have been explored in recent studies. In contrast, the individual manifestation of this effect in terms of its spatial location and extent are unclear. Using functional magnetic resonance imaging (fMRI) in 18 subjects (mean age 25.3 years), we attempted to induce LTP-like effects by HFS with checkerboard flashes at 9 Hz for 120 s. As expected, flashes induced strong activation in primary and secondary visual cortices. Contrary to our expectations, we found clusters of decreased activations induced by pattern flashes after HFS in the primary and secondary visual cortices. On the level of the individual subject, some showed significantly increased activations in the post-HFS session while the majority showed significant decreases. The locations of areas showing altered activations before and after HFS were only partly overlapping. No association between location, extent and direction of the HFS-effect was observed. The findings are unexpected in the light of existing HFS-studies, but mirror the high inter-subject variability, concerning even the directionality of the induced effects shown for other indices of LTP-like plasticity in the human brain. As this variability is not observed in LTP at the cellular level, a better understanding of LTP-like mechanisms on the macroscopic level is essential for establishing tools to quantify individual synaptic plasticity in-vivo.
authors.affiliation: Freiburg Brain Imaging, University Medical Center Freiburg Freiburg, Germany ; Department of Psychiatry and Psychotherapy, University Medical Center Freiburg Freiburg, Germany ; Department of Neurology, University Medical Center Freiburg Freiburg, Germany.
authors.forename: Jacob
authors.initials: J
authors.lastname: Lahr
authors.affiliation: Freiburg Brain Imaging, University Medical Center Freiburg Freiburg, Germany ; Department of Neurology, University Medical Center Freiburg Freiburg, Germany ; Laboratory for Biological and Personality Psychology, Department of Psychology, University of Freiburg Freiburg, Germany.
authors.forename: Jessica
authors.initials: J
authors.lastname: Peter
authors.affiliation: Eye Center, University Medical Center Freiburg Freiburg, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Bach
authors.affiliation: Department of Neuroradiology, University Medical Center Freiburg Freiburg, Germany.
authors.forename: Irina
authors.initials: I
authors.lastname: Mader
authors.affiliation: Department of Psychiatry and Psychotherapy, University Medical Center Freiburg Freiburg, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Nissen
authors.affiliation: Department of Psychiatry and Psychotherapy, University Medical Center Freiburg Freiburg, Germany.
authors.forename: Claus
authors.initials: C
authors.lastname: Normann
authors.affiliation: Freiburg Brain Imaging, University Medical Center Freiburg Freiburg, Germany ; Department of Neurology, University Medical Center Freiburg Freiburg, Germany.
authors.forename: Christoph P
authors.initials: CP
authors.lastname: Kaller
authors.affiliation: Freiburg Brain Imaging, University Medical Center Freiburg Freiburg, Germany ; Department of Psychiatry and Psychotherapy, University Medical Center Freiburg Freiburg, Germany ; Department of Neurology, University Medical Center Freiburg Freiburg, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Klöppel
keywords: LTD (long term depression); LTP (long term potentiation); VEP; fMRI (functional magnet resonance imaging); habituation; neuronal plasticity