The Effect of Perceptual Learning on Neuronal Responses in Monkey Visual Area V4

Abstract

Previous studies have shown that perceptual learning can substantially alter the response properties of neurons in the primary somatosensory and auditory cortices. Although psychophysical studies suggest that perceptual learning induces similar changes in primary visual cortex (V1), studies that have measured the response properties of individual neurons have failed to find effects of the size described for the other sensory systems. We have examined the effect of learning on neuronal response properties in a visual area that lies at a later stage of cortical processing, area V4. Adult macaque monkeys were trained extensively on orientation discrimination at a specific retinal location using a narrow range of orientations. During the course of training, the subjects achieved substantial improvement in orientation discrimination that was primarily restricted to the trained location. After training, neurons in V4 with receptive fields overlapping the trained location had stronger responses and narrower orientation tuning curves than neurons with receptive fields in the opposite, untrained hemifield. The changes were most prominent for neurons that preferred orientations close to the trained range of orientations. These results provide the first demonstration of perceptual learning modifying basic neuronal response properties at an intermediate level of visual cortex and give insights into the distribution of plasticity across adult visual cortex.

Activations in Visual and Attention-Related Areas Predict and Correlate with the Degree of Perceptual Learning

“…Schoups et al (2001) found that training of an orientation discrimination causes an increase in the slope of the tuning curve of V1 neurons. In addition, Yang and Maunsell (2004) found that the average bandwidth of the orientation tuning curve becomes narrower for the trained population of neurons in V4, especially for neurons whose preferred orientation was close to the trained orientation, a finding confirmed by Raiguel et al (2006). Moreover, in the current study, subjects who showed larger behavioral improvement also showed a greater reduction of brain activations in visual cortex.…”

“…The results, when superimposed on retinotopic maps of individual subjects, revealed that the reduced activations were seen as early as V1 but mainly in V3-V4 and beyond, all of which contain populations of neurons that are sensitive to stimulus contrast (Boynton et al, 1999;Reynolds et al, 2000;Gardner et al, 2005;Lu and Roe, 2007). Previous studies reported perceptual learning effects in early visual areas, including V1 and V4, when subjects were trained on fine discriminations of simple visual features, such as orientation and texture (Schiltz et al, 1999;Schoups et al, 2001;Schwartz et al, 2002;Furmanski et al, 2004;Yang and Maunsell, 2004;Sigman et al, 2005;Raiguel et al, 2006), and in motion-sensitive areas MT and MST, when subjects were trained on motion discrimination tasks (Zohary et al, 1994;Vaina et al, 1998). These results, together with ours, suggest that learning occurs in visual areas in which the task-relevant visual information is processed.…”

“…For example, several human imaging studies have found changes in activation in the primary visual cortex after training compared with before training on contrast discrimination (Schiltz et al, 1999), texture discrimination (Schwartz et al, 2002), contrast detection (Furmanski et al, 2004), and shape identification (Sigman et al, 2005) tasks. Single-unit recording studies of Yang and Maunsell (2004) and Raiguel et al (2006) examined the activity of neurons in visual cortical area V4 and found sharpened orientation tuning curves after training. Similarly, in motion-sensitive areas MT (middle temporal visual area) and MST (medial superior temporal visual area), Vaina et al (1998) used functional magnetic resonance imaging (fMRI) to demonstrate an expansion of the activation zone (accompanied by the disappearance of activation in other extrastriate visual areas), and Zohary et al (1994) used single-unit recordings to show an increase in neural sensitivity after human and monkey subjects, respectively, were trained on a motion discrimination task.…”

Learning-dependent plasticity with and without training in the human brain

“…In contrast, it has been shown that learning does not alter the topography or basic receptive field properties (e.g., size, location, or orientation selectivity) in V1 (34,35). Furthermore, training-dependent changes on orientation tuning are shown to be more pronounced in V4 (36,37), whereas effects in V1 are shown to be task-dependent and may engage topdown facilitation mechanisms (35,(38)(39)(40). It is possible that the lack of significant learning effects in V1 in our study is caused by the large spacing between contour elements that may prevent integration within the small receptive fields of V1 neurons.…”

Arc expression and neuroplasticity in primary auditory cortex during initial learning are inversely related to neural activity

“…These powers of neuroplasticity stem from the mammalian brain's ability to reorganize in response to experience (1)(2)(3)(4). In sensory cortex, plasticity induced by sensory tasks optimizes the brain's capacity for future performance through amplifying activity that is most informative about reinforcement (4)(5)(6). Dominant models of this plasticity are activity-dependent (2,7,8), and associated learning is presumed to be a function of endogenous processes reliant on gene activation, because long-term plasticity and long-term memory require protein synthesis (9) following expression of immediate-early genes such as Arc (10,11).…”