Neural Mechanisms of Human Perceptual Learning: Electrophysiological Evidence for a Two-Stage Process

Artículo de publicación ISIBackground: Humans and other animals change the way they perceive the world due to experience. This process has been labeled as perceptual learning, and implies that adult nervous systems can adaptively modify the way in which they process sensory stimulation. However, the mechanisms by which the brain modifies this capacity have not been sufficiently analyzed. Methodology/Principal Findings: We studied the neural mechanisms of human perceptual learning by combining electroencephalographic (EEG) recordings of brain activity and the assessment of psychophysical performance during training in a visual search task. All participants improved their perceptual performance as reflected by an increase in sensitivity (d') and a decrease in reaction time. The EEG signal was acquired throughout the entire experiment revealing amplitude increments, specific and unspecific to the trained stimulus, in event-related potential (ERP) components N2pc and P3 respectively. P3 unspecific modification can be related to context or task-based learning, while N2pc may be reflecting a more specific attentional-related boosting of target detection. Moreover, bell and U-shaped profiles of oscillatory brain activity in gamma (30-60 Hz) and alpha (8-14 Hz) frequency bands may suggest the existence of two phases for learning acquisition, which can be understood as distinctive optimization mechanisms in stimulus processing.This research was supported by CONICYT doctoral grant to C.M.H. and by an ECOS-Sud/CONICYT grant C08S02 and FONDECYT 1090612 grant to D.C. and F.A

Auditory Cortex Basal Activity Modulates Cochlear Responses in Chinchillas

Background: The auditory efferent system has unique neuroanatomical pathways that connect the cerebral cortex with sensory receptor cells. Pyramidal neurons located in layers V and VI of the primary auditory cortex constitute descending projections to the thalamus, inferior colliculus, and even directly to the superior olivary complex and to the cochlear nucleus. Efferent pathways are connected to the cochlear receptor by the olivocochlear system, which innervates outer hair cells and auditory nerve fibers. The functional role of the cortico-olivocochlear efferent system remains debated. We hypothesized that auditory cortex basal activity modulates cochlear and auditory-nerve afferent responses through the efferent system. Methodology/Principal Findings: Cochlear microphonics (CM), auditory-nerve compound action potentials (CAP) and auditory cortex evoked potentials (ACEP) were recorded in twenty anesthetized chinchillas, before, during and after auditory cortex deactivation by two methods: lidocaine microinjections or cortical cooling with cryoloops. Auditory cortex deactivation induced a transient reduction in ACEP amplitudes in fifteen animals (deactivation experiments) and a permanent reduction in five chinchillas (lesion experiments). We found significant changes in the amplitude of CM in both types of experiments, being the most common effect a CM decrease found in fifteen animals. Concomitantly to CM amplitude changes, we found CAP increases in seven chinchillas and CAP reductions in thirteen animals. Although ACE

Role of Posterior Parietal Gamma Activity in Planning Prosaccades and Antisaccades

This is a journal club article that reviews a paper by Van Der Werf et al. 2008 (http://www.jneurosci.org/cgi/content/full/28/34/8397)International audienceN.A

Schematic representation of the working model for corticofugal modulation of cochlear and auditory nerve responses produced by auditory cortex deactivation.

<p>The magnitude of cortical deactivation (green shade) produced by cryoloops (B) was larger than the one produced by lidocaine microinjections (A). Based on previous studies <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0036203#pone.0036203-Feliciano1" target="_blank">[48]</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0036203#pone.0036203-Bajo1" target="_blank">[50]</a> we propose the presence of an excitatory basal tone mediated by two groups of glutamatergic pyramidal neurons. In this model, pyramidal neurons located in auditory cortex layers V and VI project through parallel pathways to the inferior colliculus (IC). These cortical neurons are differentially deactivated (represented in light-blue) by lidocaine or cryoloops. There is indirect evidence of excitatory connections from the IC to MOC neurons <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0036203#pone.0036203-Mulders3" target="_blank">[52]</a>, but it is unknown whether there is another parallel pathway from IC to the LOC (? mark in the model). In this working model, a complete loss of descending excitatory activity will lead to CAP and CM reduction, as was observed in most cryoloop experiments. On the other hand, random deactivation of different subsets of pyramidal neurons could lead to CAP and CM enhancements or reductions, depending on the population of neurons deactivated. Blue arrows from CM to CAP represent an alternative hypothesis to explain CAP changes. Corticofugal modulation of outer hair cell activity can alter cochlear functioning and thus auditory nerve responses. (I–VI: auditory cortex layers; wm: white matter; glu: glutamate; IC: inferior colliculus).</p

CAP and CM amplitude changes in function of cortical deactivation measured by ACEP attenuation.

<p>Data from deactivation and lesion experiments were included in this figure (n = 20). <b>A.</b> Scatter plot of maximum ACEP and CAP amplitude changes. <b>B.</b> Scatter plot of maximum ACEP and CM amplitude changes. Note that CAP and CM augmentations were obtained in the same range of ACEP reductions between −10 to −20 dB, and that the cryoloop technique produced larger decreases in ACEP amplitude than lidocaine microinjections.</p

Summary of contralateral corticofugal effects obtained with lidocaine and cryoloop deactivation experiments.

<p>A scatter plot of maximum CAP and CM amplitude changes obtained with both deactivation methods is shown (green circles: lidocaine; blue squares: cryoloops). The most common effect was a simultaneous reduction in CM and CAP, observed in ten experiments. Parallel effects (correlative increases or decreases) were obtained in twelve animals, while dissociated effects were seen in three. Note that lidocaine deactivation produced diverse types of CAP and CM amplitude changes (reductions and increases), while most of the cryoloop experiments produced significant CM and CAP reductions.</p

Examples of CAP and CM changes produced in the right cochlea after lidocaine microinjection in the left auditory cortex.

<p>Cochlear potentials (CAP and CM) recorded before (black traces) and after (red traces) cortical deactivation. Both examples (A and B) were obtained from different chinchillas. <b>A.</b> Significant CAP enhancements (t = −6.42, p<0.01) and CM reductions (t = 2.51, p<0.05) after cortical microinjection of lidocaine. In this example (cx_rw_02), 4 kHz stimuli were presented at different sound pressure levels. <b>B.</b> Significant CAP and CM reductions (t = 3.62, p<0.05 and t = 2.92, p<0.05 respectively) following cortical microinjection with lidocaine. In this example (cx_rw_06), 2 kHz stimuli were presented at different sound pressure levels. Note that the corticofugal effects presented in this figure are larger with low intensity stimuli and that in both experiments we obtained CM reductions, but accompanied in one case by enhancements in CAP and in the other by reductions.</p

Effects of lidocaine microinjections on the amplitudes of auditory cortex evoked potentials.

<p>(A) Average input-output functions (n = 6) obtained at two different epochs after lidocaine microinjection (i) 10 to 20 and (ii) 50 to 60 minutes after the pharmacological deactivation (3 µl of 2% lidocaine at a rate of 1 µl/min). Note that ten to twenty minutes after the lidocaine microinjection a transient reduction in ACEP was observed, while fifty to sixty minutes after the microinjection a complete recovery was attained. 0 dB of attenuation corresponds approximately to 100 dB SPL. (B) Temporal course of lidocaine cortical deactivation. Mean auditory-cortex evoked potentials amplitude changes calculated from six chinchillas were measured at different epochs after a single lidocaine microinjection (each symbol represents mean ± standard error). A complete ACEP amplitude recovery was achieved 50 to 60 minutes after the lidocaine was given.</p

Functional selectivity in the human occipitotemporal cortex during natural vision: evidence from combined intracranial EEG and eye-tracking.

International audience: Eye movements are a constant and essential component of natural vision, yet, most of our knowledge about the human visual system comes from experiments that restrict them. This experimental constraint is mostly in place to control visual stimuli presentation and to avoid artifacts in non-invasive measures of brain activity, however, this limitation can be overcome with intracranial EEG (iEEG) recorded from epilepsy patients. Moreover, the high-frequency components of the iEEG signal (between about 50 and 150Hz) can provide a proxy of population-level spiking activity in any cortical area during free-viewing. We combined iEEG with high precision eye-tracking to study fine temporal dynamics and functional specificity in the fusiform face (FFA) and visual word form area (VWFA) while patients inspected natural pictures containing faces and text. We defined the first local measure of visual (electrophysiological) responsiveness adapted to free-viewing in humans: amplitude modulations in the high-frequency activity range (50-150Hz) following fixations (fixation-related high-frequency response). We showed that despite the large size of receptive fields in the ventral occipito-temporal cortex, neural activity during natural vision of realistic cluttered scenes is mostly dependent upon the category of the foveated stimulus - suggesting that category-specificity is preserved during free-viewing and that attention mechanisms might filter out the influence of objects surrounding the fovea