Scientific Understanding of Consciousness
Perceptual Learning in Early Visual Cortex
Science 9 December 2011: Vol. 334 no. 6061 pp. 1413-1415
Perceptual Learning Incepted by Decoded fMRI Neurofeedback Without Stimulus Presentation
Kazuhisa Shibata, Takeo Watanabe, Yuka Sasaki, Mitsuo Kawato
Advanced Telecommunications Research Institute International Computational Neuroscience Laboratories, 2-2-2 Hikaridai, Keihanna Science City, Kyoto 619-0288, Japan.
It is controversial whether the adult primate early visual cortex is sufficiently plastic to cause visual perceptual learning (VPL). The controversy occurs partially because most VPL studies have examined correlations between behavioral and neural activity changes rather than cause-and-effect relationships. With an online-feedback method that uses decoded functional magnetic resonance imaging (fMRI) signals, we induced activity patterns only in early visual cortex corresponding to an orientation without stimulus presentation or participants’ awareness of what was to be learned. The induced activation caused VPL specific to the orientation. These results suggest that early visual areas are so plastic that mere inductions of activity patterns are sufficient to cause VPL. This technique can induce plasticity in a highly selective manner, potentially leading to powerful training and rehabilitative protocols.
Whether adult primate visual cortex has sufficient plasticity to allow for behavioral and/or sensitivity changes remains a point of great controversy. Many studies have examined how activity changes in the brain are correlated with performance improvements on a visual task resulting from repetitive training, known as visual perceptual learning. However, such a correlational approach has not conclusively settled the adult plasticity debate. Although some studies have found correlations between performance increase and changes in early visual areas, other studies found correlations in higher visual and/or decision areas. None of these studies directly addresses the question of whether early visual areas are sufficiently plastic to cause VPL.
To address the question of whether early visual areas are that plastic, we developed a functional magnetic resonance imaging (fMRI) online-feedback method, by which activation patterns corresponding to the pattern evoked by the presentation of a real and specific target orientation stimulus were repeatedly induced without the participants’ knowledge of what is being learned and without external stimulus presentation. The mere induction of the activation patterns resulted in significant behavioral performance improvement on the target stimulus orientation, but not on other orientations.
The complete experiment consisted of four stages: (i) pre-test (1 day), (ii) fMRI decoder construction (1 day), (iii) induction (decoded fMRI neurofeedback, 5 days for four participants and 10 days for six participants), and (iv) post-test (1 day) stages.
We tried to obtain fMRI activity patterns in V1/V2 that are induced by the presentation of each of the three tested orientations in Gabor patches for each participant (fMRI decoder construction stage). Participants were asked to perform a task designed to maintain their attention to the Gabor patches while fMRI signals in V1/V2 were measured. Based on the fMRI signals, we constructed a multinomial sparse logistic regression decoder to classify a pattern of the measured fMRI signals into one of the three orientations.
Once the decoder was constructed, each participant took part in a 5- or 10-day induction stage during which he or she learned to induce activation patterns in V1/V2 that corresponded to the target orientation, one of the three orientations, that was randomly assigned to each participant.
The purpose of the induction stage was to have participants learn and then continue to induce activity patterns with significantly high target-orientation likelihood in V1/V2. The main purpose of the present study was to examine whether the mere repetitive induction of specific activation patterns in V1/V2 causes VPL reflected as performance improvement.
Our results indicate that the adult early visual cortex is so plastic that mere repetition of the activity pattern corresponding to a specific feature in the cortex is sufficient to cause VPL of a specific orientation, even without stimulus presentation, conscious awareness of the meaning of the neural patterns that participants induced, or knowledge of the intention of the experiment.
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