Induction of orientation-specific LTP-like changes in human visual evoked potentials by rapid sensory stimulation.

Recent research suggests that rapid visual stimulation can induce long-term potentiation-like effects non-invasively in humans. However, to date, this research has provided only limited evidence for input-specificity, a fundamental property of cellular long-term potentiation. In the present study we extend the evidence for input-specificity by investigating the effect of stimulus orientation. We use sine wave gratings of two different orientations to show that rapid visual stimulation can induce orientation-specific potentiation, as indexed by changes in the amplitude of a late phase of the N1 complex of the visual-evoked potential. This result suggests that discrete populations of orientation-tuned neurons can be selectively potentiated by rapid visual stimulation. Furthermore, our results support earlier studies that have suggested that the locus of potentiation induced by rapid visual stimulation is visual cortex.

Spatial frequency-specific potentiation of human visual-evoked potentials.

Recent research has suggested that cortical long-term potentiation can be induced non-invasively in humans by using rapid visual stimulation. The present study extends these findings by investigating the specificity of this long-term potentiation effect to the inducing stimulus. One group of study participants were tetanized using a one cycle-per-degree sine grating, while a second group was tetanized using a five cycles-per-degree sine grating. Using electroencephalography, we found that an increase in the N1b potential was specific to sine gratings of the same frequency as the tetanus. No effect was observed in the N1b for sine gratings of a different spatial frequency. These results suggest that the long-term potentiation effect induced by the sensory tetanus is isolated to a discrete neural population in the visual cortex.

Rapid visual stimulation induces N-methyl-D-aspartate receptor-dependent sensory long-term potentiation in the rat cortex.

Previously we have demonstrated that rapidly presented sensory stimulation (visual or auditory) can induce long-lasting increases in sensory evoked potentials recorded from the human cortex. Long-term potentiation was suggested as the underlying mechanism of these increases. In the present experiment, we applied the same visual paradigm to anesthetized rats to investigate the properties and mechanisms of this effect. Our results indicated that visual evoked responses were significantly enhanced for at least 1 h and, when followed, up to 5 h after the presentation of a 'photic tetanus.' Furthermore, the potentiation was N-methyl-D-aspartate receptor-dependent and cortically generated. This type of sensory long-term potentiation may underlie perceptual learning, and serves as a model system for investigating sensory-evoked plasticity.

Long-term enhanced desynchronization of the alpha rhythm following tetanic stimulation of human visual cortex.

It had been shown previously that a photic tetanus induces LTP-like changes in the visual cortex, as indexed by an enhancement of the N1b component of the visual evoked potential, recorded non-invasively by electroencephalography. This potentiation was shown to last over 1 h. In the present study, the effect of a photic tetanus on oscillatory activity is investigated. EEGs were collected from eight healthy subjects in three conditions while visual checkerboards were displayed. Following baseline presentations in two conditions a lateralized visual tetanus was given, either to the left or right visual field, and in a third condition no tetanus was given. This was followed by a return to baseline presentations, both immediately after the tetanus/control block, and 1 h later. Enhanced event-related desynchronization (ERD) of the alpha rhythm lasting 1 h was seen following the photic tetanus over occipital electrodes. Because ERD of the alpha rhythm is thought to represent active cortex, these results suggest that the visual tetanus induces long-lasting cortical changes, with stronger neuronal assemblies and increased neuronal output.

Effects of long-term potentiation in the human visual cortex: a functional magnetic resonance imaging study.

Applying functional magnetic resonance imaging techniques, hemodynamic responses elicited by slowly flashing checkerboards (0.25 Hz) were measured both before and after a block of rapidly presented checkerboards (9 Hz -- a 'photic tetanus') was delivered. It has been shown previously, using electroencephalography, that this photic tetanus potentiates components of the visual-evoked potential. In the present study, hemodynamic responses in the extrastriate visual cortex were significantly increased to checkerboards presented at a low frequency after the administration of the photic tetanus. These results support the idea that long-term potentiation can be demonstrated non-invasively within the human visual cortex and provide evidence that the plastic changes are localized within the secondary visual cortex.