Alterations of brain activity and functional connectivity in transition from acute to chronic tinnitus

The objective of this study was to investigate alterations to brain activity and functional connectivity in patients with tinnitus, exploring neural features in the transition from acute to chronic phantom perception. Twenty‐four patients with acute tinnitus, 23 patients with chronic tinnitus, and 32 healthy controls were recruited. High‐density electroencephalography (EEG) was used to explore changes in brain areas and functional connectivity in different groups. When compared with healthy subjects, acute tinnitus patients had a significant reduction in superior frontal cortex activity across all frequency bands, whereas chronic tinnitus patients had a significant reduction in the superior frontal cortex at beta 3 and gamma frequency bands as well as a significant increase in the inferior frontal cortex at delta‐band and superior temporal cortex at alpha 1 frequency band. When compared to the chronic tinnitus group, the acute tinnitus group activity was significantly increased in the middle frontal and parietal gyrus at the gamma‐band. Functional connectivity analysis showed that the chronic tinnitus group had increased connections between the parahippocampus gyrus, posterior cingulate cortex, and precuneus when compared with the healthy group. Alterations of local brain activity and connections between the parahippocampus gyrus and other nonauditory areas appeared in the transition from acute to chronic tinnitus. This indicates that the appearance and development of tinnitus is a dynamic process involving aberrant local neural activity and abnormal connectivity in multifunctional brain networks.     

Reductions in cortical alpha activity,enhancements in neural responses and impaired gap detection caused by sodium salicylate in awake guinea pigs

Tinnitus chronically affects between 10–15% of the population but, despite its prevalence, the underlying mechanisms are still not properly understood. One experimental model involves administration of high doses of sodium salicylate, as this is known to reliably induce tinnitus in both humans and animals. Guinea pigs were implanted with chronic electrocorticography (ECoG) electrode arrays, with silver‐ball electrodes placed on the dura over left and right auditory cortex. Two more electrodes were positioned over the cerebellum to monitor auditory brainstem responses (ABRs). We recorded resting‐state and auditory evoked neural activity from awake animals before and 2 h following salicylate administration (350 mg/kg; i.p.). Large increases in click‐evoked responses (> 100%) were evident across the whole auditory cortex, despite significant reductions in wave I ABR amplitudes (in response to 20 kHz tones), which are indicative of auditory nerve activity. In the same animals, significant decreases in 6–10 Hz spontaneous oscillations (alpha waves) were evident over dorsocaudal auditory cortex. We were also able to demonstrate for the first time that cortical evoked potentials can be inhibited by a preceding gap in background noise [gap‐induced pre‐pulse inhibition (PPI)], in a similar fashion to the gap‐induced inhibition of the acoustic startle reflex that is used as a behavioural test for tinnitus. Furthermore, 2 h following salicylate administration, we observed significant deficits in PPI of cortical responses that were closely aligned with significant deficits in behavioural responses to the same stimuli. Together, these data are suggestive of neural correlates of tinnitus and oversensitivity to sound (hyperacusis).     

Hearing an illusory vowel in noise: suppression of auditory cortical activity

Human hearing is constructive. For example, when a voice is partially replaced by an extraneous sound (e.g., on the telephone due to a transmission problem), the auditory system may restore the missing portion so that the voice can be perceived as continuous (Miller and Licklider, 1950; for review, see Bregman, 1990; Warren, 1999). The neural mechanisms underlying this continuity illusion have been studied mostly with schematic stimuli (e.g., simple tones) and are still a matter of debate (for review, see Petkov and Sutter, 2011). The goal of the present study was to elucidate how these mechanisms operate under more natural conditions. Using psychophysics and electroencephalography (EEG), we assessed simultaneously the perceived continuity of a human vowel sound through interrupting noise and the concurrent neural activity. We found that vowel continuity illusions were accompanied by a suppression of the 4 Hz EEG power in auditory cortex (AC) that was evoked by the vowel interruption. This suppression was stronger than the suppression accompanying continuity illusions of a simple tone. Finally, continuity perception and 4 Hz power depended on the intactness of the sound that preceded the vowel (i.e., the auditory context). These findings show that a natural sound may be restored during noise due to the suppression of 4 Hz AC activity evoked early during the noise. This mechanism may attenuate sudden pitch changes, adapt the resistance of the auditory system to extraneous sounds across auditory scenes, and provide a useful model for assisted hearing devices.     

The neural network of phantom sound changes over time: a comparison between recent-onset and chronic tinnitus patients

Tinnitus is characterized by an ongoing conscious perception of a sound in the absence of any external sound source. Chronic tinnitus is notoriously characterized by its resistance to treatment. In the present study the objective was to verify whether the neural generators and/or the neural tinnitus network, evaluated through EEG recordings, change over time as previously suggested by MEG. We therefore analyzed the source-localized EEG recordings of a very homogenous group of left-sided narrow-band noise tinnitus patients. Results indicate that the generators involved in tinnitus of recent onset seem to change over time with increased activity in several brain areas [auditory cortex, supplementary motor area and dorsal anterior cingulate cortex (dACC) plus insula], associated with a decrease in connectivity between the different auditory and nonauditory brain structures. An exception to this general connectivity decrease is an increase in gamma-band connectivity between the left primary and secondary auditory cortex and the left insula, and also between the auditory cortices and the right dorsal lateral prefrontal cortex. These networks are both connected to the left parahippocampal area. Thus acute and chronic tinnitus are related to differential activity and connectivity in a network comprising the auditory cortices, insula, dACC and premotor cortex.     

Brain mapping of auditory hallucinations and illusions induced by direct intracortical electrical stimulation

BackgroundThe exact architecture of the human auditory cortex remains a subject of debate, with discrepancies between functional and microstructural studies. In a hierarchical framework for sensory perception, simple sound perception is expected to take place in the primary auditory cortex, while the processing of complex, or more integrated perceptions is proposed to rely on associative and higher-order cortices.ObjectivesWe hypothesize that auditory symptoms induced by direct electrical stimulation (DES) offer a window into the architecture of the brain networks involved in auditory hallucinations and illusions. The intracranial recordings of these evoked perceptions of varying levels of integration provide the evidence to discuss the theoretical model.MethodsWe analyzed SEEG recordings from 50 epileptic patients presenting auditory symptoms induced by DES. First, using the Juelich cytoarchitectonic parcellation, we quantified which regions induced auditory symptoms when stimulated (ROI approach). Then, for each evoked auditory symptom type (illusion or hallucination), we mapped the cortical networks showing concurrent high-frequency activity modulation (HFA approach).ResultsAlthough on average, illusions were found more laterally and hallucinations more posteromedially in the temporal lobe, both perceptions were elicited in all levels of the sensory hierarchy, with mixed responses found in the overlap. The spatial range was larger for illusions, both in the ROI and HFA approaches. The limbic system was specific to the hallucinations network, and the inferior parietal lobule was specific to the illusions network.DiscussionOur results confirm a network-based organization underlying conscious sound perception, for both simple and complex components. While symptom localization is interesting from an epilepsy semiology perspective, the hallucination-specific modulation of the limbic system is particularly relevant to tinnitus and schizophrenia.     

Effects of individual alpha rTMS applied to the auditory cortex and its implications for the treatment of chronic tinnitus

An increasing amount of studies apply repetetive transcranial magnetic stimulation (rTMS) to treat chronic tinnitus, yet the neurophysiological impacts have remained largely obscure. Several studies show that endogenous brain rhythms may be enhanced via diverse brain stimulation techniques applying rhythmic stimulation. Here, we investigated in normal hearing participants whether application of rTMS (left auditory cortex) with an individualized alpha frequency was capable of increasing alpha activity in stimulated auditory regions in a sustained manner. Behavioral intensity discrimination performance worsened for the rTMS group as compared to Sham. Electroencephalography (EEG) data, however, clearly show that this functional inhibition is not accompanied by increases of auditory cortical alpha. Even though more pronounced power reductions for the rTMS group were observed at slower frequencies (delta to theta range) at stimulated and other sites of the left hemisphere, they were unrelated to behavioral changes. Our results also strongly suggest that the amount of power modulations at these slower frequencies is strongly dependent on pre‐rTMS power, thus supporting current state‐dependency notions. Strong relationships to behavioral changes were in particular observed for anterior cingulate cortex (ACC) beta power and posterior cingulate cortex (PCC) beta connectivity. Moreover, these beta band measures were strongly inter‐related and when viewed together specifically sensitive to behavioral changes in the rTMS group. We conclude that currently alpha frequency rTMS is not a promising avenue for the treatment of chronic tinnitus and that beneficial effects could be mediated via nonauditory systems. Our study argues for the value of combined EEG‐TMS studies when investigating the impacts of rTMS. Hum Brain Mapp 35:14–29, 2014. © 2012 Wiley Periodicals, Inc.     

Hearing Safety of Long-Term Treatment with Theta Burst Stimulation

BackgroundRepetitive transcranial magnetic stimulation (rTMS) for the experimental treatment of tinnitus or auditory hallucinations aims at a modulation of cortical activity in areas of auditory perception and processing. Continuous theta burst stimulation (cTBS) is a patterned rTMS paradigm with lower stimulation intensity and shorter stimulus duration that is increasingly used for the optimization of rTMS-treatment paradigms. Possible interference with physiological brain function and the noise emitted by the rTMS device might induce relevant unwanted impairment of hearing and speech perception.Objective/HypothesisHere, we investigate the audiological safety of long-term, bilateral cTBS for the treatment of auditory phantom perception.MethodsForty-eight patients with chronic tinnitus were treated for four weeks with bilateral continuous theta burst stimulation to the temporal (n = 16), temporoparietal (n = 16) or a non-cortical control (n = 16) site. Measurements in these patients were obtained before and four weeks after treatment. The rTMS-induced noise was measured at various frequency levels.ResultsNo evidence was found for auditory threshold shifts or alterations in the perception of speech in quiet or in background noise by bilateral, long-term theta burst stimulation to the temporal or temporoparietal cortex with a loudness of up to 84 dB SPL (A).ConclusionsTheta burst stimulation of the temporal and temporoparietal cortex appears to be safe with respect to hearing and speech perception. These data provide evidence for the audiological safety of rTMS in the experimental treatment of auditory phantom perception.     

Rapid increases of gamma power in the auditory cortex following noise trauma in humans

Tinnitus is an auditory perception in the absence of any external sound source. It has been suggested that tinnitus is related to enhanced synchronization of neuronal activity in the auditory cortex. Usually a hearing damage can be identified suggesting auditory deprivation to central auditory regions to be fundamental for neurophysiological processes related to tinnitus. Until now, human research has been conducted on patients with chronic tinnitus (>6 months). However, neuronal activity accompanying auditory deprivation and putatively tinnitus may not remain constant over time, making it difficult to directly relate outcomes of current animal studies (acute tinnitus) to chronic tinnitus in humans, and vice versa. We investigated 14 amateur rock musicians who frequently reported a short-term tinnitus immediately after band practice. Magnetoencephalographic resting-state recordings, audiometry and tinnitus testing were performed at two separate occasions: with and without previous exposure to loud music. Analyses revealed that transient tinnitus was accompanied by temporary hearing loss in both ears and increased gamma activity in the right auditory cortex in 13 out of 14 cases. Additionally, tinnitus frequency was strongly correlated to hearing loss. Analogous to animal studies, our results show for the first time in humans that noise trauma leads rapidly to increased neuronal synchrony in the auditory cortex. Importantly, the strongly right-lateralized effect implies that it does not reflect tinnitus percept per se. This could rather have been triggered by greater discontinuities of hearing loss at high frequencies that were particularly pronounced in the left ear.     

Illusions: a window into perception

Perception is the active construction of a neural state that correlates with biologically relevant elements present in the environment. This correlation, far from affording a one-to-one mapping, nonetheless guides our actions towards adaptive behaviors, thus being forged under evolutionary constraints. Since the construction of a percept is an intrinsically ambiguous process, perceptual discrepancies can arise from identical stimulation patterns. The recognition of these discrepancies is termed illusion, which originates, however, from the same physiological mechanisms that ordinarily lead to standard perception. Emanating from different sources, such as optical, sensory and cognitive factors, visual illusions are useful tools in accessing the physiological basis of perceptual processes and their interaction with motor planning and execution. Here we examine the biological roots of visual illusions and their interplay with some neurobiological, philosophical and esthetical issues.     

Switching Tinnitus-On: Maps and source localization of spontaneous EEG

ObjectiveTo identify the spectrotemporal changes and sources in patients that could “turn on” tinnitus with multichannel electroencephalography (EEG) system.MethodsMultichannel EEG was recorded from six patients during the Tinnitus-On and Tinnitus-Off states. The EEG power spectrum and eLORETA-based sources were measured.ResultsThere was a global increase in delta and theta during Tinnitus-On plus large changes in alpha 1 and alpha 2. During the Tinnitus-On state, many new sources in delta, theta, alpha 1 and gamma bands emerged in the opposite hemisphere in the inferior temporal gyrus (Brodmann area, BA 20), middle temporal gyrus (BA 21), lateral perirhinal cortex (BA 36), ventral entorhinal cortex (BA 28) and anterior pole of the temporal gyrus (BA 38).ConclusionsThe emergence of new delta, theta and gamma band sources in the inferior temporal gyrus (BA 20), middle temporal gyrus (BA 21) and lateral perirhinal cortex (BA 36) plus the appearance of new delta and theta sources in the ventral entorhinal cortex (BA28) and anterior pole of the temporal lobe (BA 38) may comprise a network capable of evoking the phantom sound of tinnitus by simultaneously engaging brain regions involved in memory, sound recognition, and distress which together contribute to tinnitus severity.SignificanceThe sudden appearance of new sources of activity in the opposite hemisphere within the inferior temporal gyrus, middle temporal gyrus and perirhinal cortex may initiate the perception of tinnitus perception.     

Neurophysiological correlates of residual inhibition in tinnitus: Hints for trait-like EEG power spectra

ObjectiveTo investigate oscillatory brain activity changes following acoustic stimulation in tinnitus and whether these changes are associated with behavioral measures of tinnitus loudness. Moreover, differences in ongoing brain activity between individuals with and without residual inhibition (RI) are examined (responders vs. non-responders).MethodsThree different types of noise stimuli were administered for acoustic stimulation in 45 tinnitus patients. Subjects resting state brain activity was recorded before and after stimulation via EEG alongside with subjective measurements of tinnitus loudness.ResultsDelta, theta and gamma band power increased, whereas alpha and beta power decreased from pre to post stimulation. Acoustic stimulation responders exhibited reduced gamma and a trend for enhanced alpha activity with the latter localized in the right inferior temporal gyrus. Post stimulation, individuals experiencing RI showed higher theta, alpha and beta power with a peak power difference in the alpha band localized in the right superior temporal gyrus. Neither correlations with behavioral tinnitus measures nor stimulus-specific changes in EEG activity were present.ConclusionsOur observations might be indicative of trait-specific forms of oscillatory signatures in different subsets of the tinnitus population related to acoustic tinnitus suppression.SignificanceResults and insights are not only useful to understand basic neural mechanisms behind RI but are also valuable for general neural models of tinnitus.     

A novel behavioral assay for the assessment of acute tinnitus in rats optimized for simultaneous recording of oscillatory neural activity

Background

Human magneto/electrophysiology studies suggest that the phantom sound of tinnitus arises from spontaneous oscillatory neural activity in auditory cortex; however, in animal models, behavioral techniques suitable for testing this hypothesis in combination with electrophysiology recordings have yet to be evaluated. While electrophysiological studies of tinnitus have been reported in passive, awake animals, these studies fail to control for attentional mechanisms likely to play a role in the perception of tinnitus.

New method

A novel appetitive operant conditioning, two-alternative identification task was developed for detecting acute tinnitus in rats. The procedure optimizes conditions for simultaneously recording oscillatory neural activity while controlling for the attentional state of the animal.

Results

Tinnitus was detected in six of seven rats following systemic injection with sodium salicylate (200 mg/kg IP), a known inducer of tinnitus. Analysis of ongoing local field potentials recorded from chronically implanted electrodes in auditory cortex of a rat reporting tinnitus revealed changes in the spectrum of ongoing neural activity.Comparison with existing method(s): Existing tinnitus-detection methods were not explicitly designed for the simultaneous recording of neural activity. The behavioral method reported here is the first to provide the conditions necessary for obtaining these recordings in chronically implanted rats.

Conclusions

The behavioral assay presented here will facilitate research into the neural mechanisms of tinnitus by allowing researchers to compare the electrophysiological data in animals with confirmed tinnitus.     

A selective imaging of tinnitus

We selectively imaged the neural correlates of tinnitus, by contrasting a condition with no phantom auditory sensation with a condition during which tinnitus is present, using a rare form of tinnitus elicited by eye movements. Using positron emission tomography (PET), we demonstrate that phantom auditory sensation increases regional cerebral blood flow bilaterally in temporo-parietal association auditory areas but not in the primary auditory cortex. These results confirm that conscious perception does not necessarily require activation in primary areas and suggest that the perceptual qualities of tinnitus, e.g. intensity, frequency and spatial localization, are represented in temporo-parietal regions. Activation in these regions is compatible with cortical processing of ascending auditory messages generated at subcortical levels.     

Representation of illusory and physical rotations in human MST: A cortical site for the pinna illusion

Visual illusions have fascinated mankind since antiquity, as they provide a unique window to explore the constructive nature of human perception. The Pinna illusion is a striking example of rotation perception in the absence of real physical motion. Upon approaching or receding from the Pinna‐Brelstaff figure, the observer experiences vivid illusory counter rotation of the two rings in the figure. Although this phenomenon is well known as an example of integration from local cues to a global percept, the visual areas mediating the illusory rotary perception in the human brain have not yet been identified. In the current study we investigated which cortical area in the human brain initially mediates the Pinna illusion, using psychophysical tests and functional magnetic resonance imaging (fMRI) of visual cortices V1, V2, V3, V3A, V4, and hMT+ of the dorsal and ventral visual pathways. We found that both the Pinna‐Brelstaff figure (illusory rotation) and a matched physical rotation control stimulus predominantly activated subarea MST in hMT+ with a similar response intensity. Our results thus provide neural evidence showing that illusory rotation is initiated in human MST rather than MT as if it were physical rotary motion. The findings imply that illusory rotation in the Pinna illusion is mediated by rotation‐sensitive neurons that normally encode physical rotation in human MST, both of which may rely on a cascade of similar integrative processes from earlier visual areas. Hum Brain Mapp 37:2097–2113, 2016. © 2016 Wiley Periodicals, Inc.     

Frontostriatal network dysfunction as a domain‐general mechanism underlying phantom perception

In the present study, we use resting state fMRI to investigate whether nucleus accumbens (NAc) and extended frontostriatal networks are involved in the pathology of auditory phantom perception, i.e., tinnitus, through a study of functional connectivity. We hypothesize that resting state functional connectivity involving NAc will be increased relative to what is observed in healthy subjects and that this connectivity will correlate with clinical measures of tinnitus such as percept loudness, duration of symptoms, etc. We show that a large sample of patients with chronic tinnitus (n = 90) features extensive functional connectivity involving NAc that is largely absent in healthy subjects (n = 94). We further show that connectivity involving NAc correlates significantly with tinnitus percept loudness and the duration of tinnitus symptoms, even after controlling for the effects of age and hearing loss. The loudness correlation, which involves NAc and parahippocampal cortex, is consistent with existing literature identifying the parahippocampus as a tinnitus generator. Our results further suggest that frontostriatal connectivity may predict the transition from acute to chronic tinnitus, analogous to what is seen in the pain literature. We discuss these ideas and suggest fruitful avenues for future research.     

Remodeling of cholinergic input to the hippocampus after noise exposure and tinnitus induction in Guinea pigs

Here, we investigate remodeling of hippocampal cholinergic inputs after noise exposure and determine the relevance of these changes to tinnitus. To assess the effects of noise exposure on the hippocampus, guinea pigs were exposed to unilateral noise for 2 hr and 2 weeks later, immunohistochemistry was performed on hippocampal sections to examine vesicular acetylcholine transporter (VAChT) expression. To evaluate whether the changes in VAChT were relevant to tinnitus, another group of animals was exposed to the same noise band twice to induce tinnitus, which was assessed using gap‐prepulse Inhibition of the acoustic startle (GPIAS) 12 weeks after the first noise exposure, followed by immunohistochemistry. Acoustic Brainstem Response (ABR) thresholds were elevated immediately after noise exposure for all experimental animals but returned to baseline levels several days after noise exposure. ABR wave I amplitude‐intensity functions did not show any changes after 2 or 12 weeks of recovery compared to baseline levels. In animals assessed 2‐weeks following noise‐exposure, hippocampal VAChT puncta density decreased on both sides of the brain by 20–60% in exposed animals. By 12 weeks following the initial noise exposure, changes in VAChT puncta density largely recovered to baseline levels in exposed animals that did not develop tinnitus, but remained diminished in animals that developed tinnitus. These tinnitus‐specific changes were particularly prominent in hippocampal synapse‐rich layers of the dentate gyrus and areas CA3 and CA1, and VAChT density in these regions negatively correlated with tinnitus severity. The robust changes in VAChT labeling in the hippocampus 2 weeks after noise exposure suggest involvement of this circuitry in auditory processing. After chronic tinnitus induction, tinnitus‐specific changes occurred in synapse‐rich layers of the hippocampus, suggesting that synaptic processing in the hippocampus may play an important role in the pathophysiology of tinnitus.     

Human limb-specific and non-limb-specific brain representations during kinesthetic illusory movements of the upper and lower extremities

Sensing movements of the upper and lower extremities is important in controlling whole-body movements. We have shown that kinesthetic illusory hand movements activate motor areas and right-sided fronto-parietal cortices. We investigated whether illusions for the upper and lower extremities, i.e. right or left hand or foot, activate the somatotopical sections of motor areas, and if an illusion for each limb engages the right-sided cortices. We scanned the brain activity of 19 blindfolded right-handed participants using functional magnetic resonance imaging (fMRI) while they experienced an illusion for each limb elicited by vibrating its tendon at 110 Hz (ILLUSION). As a control, we applied identical stimuli to the skin over a nearby bone, which does not elicit illusions (VIBRATION). The illusory movement (ILLUSION vs. VIBRATION) of each immobile limb activated limb-specific sections of the contralateral motor cortex (along with somatosensory area 3a), dorsal premotor cortex (PMD), supplementary motor area (SMA), cingulate motor area (CMA), and the ipsilateral cerebellum, which normally participate in execution of movements of the corresponding limb. We found complex non-limb-specific representations in rostral parts of the bilateral SMA and CMA, and illusions for all limbs consistently engaged concentrated regions in right-sided fronto-parietal cortices and basal ganglia. This study demonstrated complete sets of brain representations related to kinesthetic processing of single-joint movements of the four human extremities. The kinesthetic function of motor areas suggests their importance in somatic perception of limb movement, and the non-limb-specific representations indicate high-order kinesthetic processing related to human somatic perception of one's own body.     

Perception of the auditory‐visual illusion in speech perception by children with phonological disorders

An example of the auditory‐visual illusion in speech perception, first described by McGurk and MacDonald, is the perception of [ta] when listeners hear [pa] in synchrony with the lip movements for [ka]. One account of the illusion is that lip‐read and heard speech are combined in an articulatory code since people who mispronounce words respond differently from controls on lip‐reading tasks. A same‐different judgment task assessing perception of the illusion showed no difference in performance between controls and children with speech difficulties. Another experiment compared children with delayed and disordered speech on perception of the illusion. While neither group perceived many illusions, a significant interaction indicated that children with disordered phonology were strongly biased to the auditory component while the delayed group's response was more evenly split between the auditory and visual components of the illusion. These findings suggest that phonological processing, rather than articulation, supports lip‐reading ability.     

Visual illusions, delayed grasping, and memory: no shift from dorsal to ventral control

We tested whether a delay between stimulus presentation and grasping leads to a shift from dorsal to ventral control of the movement, as suggested by the perception-action theory of Milner and Goodale (Milner, A.D., & Goodale, M.A. (1995). The visual brain in action. Oxford: Oxford University Press.). In this theory the dorsal cortical stream has a short memory, such that after a few seconds the dorsal information is decayed and the action is guided by the ventral stream. Accordingly, grasping should become responsive to certain visual illusions after a delay (because only the ventral stream is assumed to be deceived by these illusions). We used the Müller-Lyer illusion, the typical illusion in this area of research, and replicated the increase of the motor illusion after a delay. However, we found that this increase is not due to memory demands but to the availability of visual feedback during movement execution which leads to online corrections of the movement. Because such online corrections are to be expected if the movement is guided by one single representation of object size, we conclude that there is no evidence for a shift from dorsal to ventral control in delayed grasping of the Müller-Lyer illusion. We also performed the first empirical test of a critique Goodale (Goodale, M.A. (2006, October 27). Visual duplicity: Action without perception in the human visual system. The XIV. Kanizsa lecture, Triest, Italy.) raised against studies finding illusion effects in grasping: Goodale argued that these studies used methods that lead to unnatural grasping which is guided by the ventral stream. Therefore, these studies might never have measured the dorsal stream, but always the ventral stream. We found clear evidence against this conjecture.     

Environmental enrichment rescues the degraded auditory temporal resolution of cortical neurons induced by early noise exposure

The accurate processing of sound temporal information is crucial to human speech perception and other species‐specific communication. During postnatal development, the auditory cortex shows environmental and experience‐dependent plasticity. However, how the postnatal environment affects cortical processing of sound temporal information is not fully understood. The aim of the present study was to determine whether postnatal noise exposure impairs neural temporal resolution in the auditory cortex, and, if so, whether environmental enrichment can rescue this degraded neural temporal acuity. Using the neural gap detection threshold determined in anesthetized rats as an index of temporal acuity, we found that exposure of juvenile rats to moderate‐level noise induced much higher neural gap detection thresholds in adulthood than exposure of adult rats to the same noise. Environmental enrichment did not affect cortical neural gap detection thresholds in normally developing rats. However, rearing of rats with early noise exposure in an enriched environment promoted recovery from the noise‐induced degraded neural temporal resolution. In addition, the tonal stimuli in the enriched environment contributed to only a portion of the recovery. These results provide evidence for noise‐induced developmental impairment in neural gap detection thresholds in the auditory cortex, and suggest a therapeutic potential for environmental enrichment as a non‐invasive approach to rescue developmentally degraded auditory temporal processing.