Recognition of interleaved melodies. An fMRI study

Simultaneous auditory agnosia: Systematic description of a new type of auditory segregation deficit following a right hemisphere lesion

We investigated auditory processing in a young patient who experienced a single embolus causing an infarct in the right middle cerebral artery territory. This led to damage to auditory cortex including planum temporale that spared medial Heschl's gyrus, and included damage to the posterior insula and inferior parietal lobule. She reported chronic difficulties with segregating speech from noise and segregating elements of music. Clinical tests showed no evidence for abnormal cochlear function. Follow-up tests confirmed difficulties with auditory segregation in her left ear that spanned multiple domains, including words-in-noise and music streaming. Testing with a stochastic figure-ground task-a way of estimating generic acoustic foreground and background segregation-demonstrated that this was also abnormal. This is the first demonstration of an acquired deficit in the segregation of complex acoustic patterns due to cortical damage, which we argue is a causal explanation for the symptomatic deficits in the segregation of speech and music. These symptoms are analogous to the visual symptom of simultaneous agnosia. Consistent with functional imaging studies on normal listeners, the work implicates non-primary auditory cortex. Further, the work demonstrates a (partial) lateralisation of the necessary anatomical substrate for segregation that has not been previously highlighted.

Differential Activation and Functional Plasticity of Multimodal Areas Associated with Acquired Musical Skill

Training of a musical skill is known to produce a distributed neural representation of the ability to perceive music and perform musical tasks. In the present study we tested the hypothesis that the audiovisual perception of music involves a wider activation of multimodal sensory and sensorimotor structures in the brain, including those containing mirror neurons. We mapped the activation of brain areas during passive listening and viewing of the first 40 s of "Ode to Joy" being played on the piano by an expert pianist. To do this we performed brain functional magnetic resonance imaging during the presentation of 6 different stimulus contrasts pertaining to that musical melody in a pseudo-randomized order. Group data analysis in musically trained and untrained adults showed robust activation in broadly distributed occipitotemporal, parietal and frontal areas in trained subjects and much restricted activation in untrained subjects. A visual stimulus contrast focusing on the visual motion percept of moving fingers on piano keys revealed selective bilateral activation of a locus corresponding to the V5/MT area, which was significantly more pronounced in trained subjects and showed partial linear dependence on the duration of training on the left side. Quantitative analysis of individual brain volumes confirmed a significantly greater and wider spread of activation in trained compared to untrained subjects. These findings support the view that audiovisual perception of music and musical gestures in trained musicians involves an expanded and widely distributed neural representation formed due to experience-dependent plasticity.

Music Perception in Dementia

Despite much recent interest in music and dementia, music perception has not been widely studied across dementia syndromes using an information processing approach. Here we addressed this issue in a cohort of 30 patients representing major dementia syndromes of typical Alzheimer's disease (AD, n = 16), logopenic aphasia (LPA, an Alzheimer variant syndrome; n = 5), and progressive nonfluent aphasia (PNFA; n = 9) in relation to 19 healthy age-matched individuals. We designed a novel neuropsychological battery to assess perception of musical patterns in the dimensions of pitch and temporal information (requiring detection of notes that deviated from the established pattern based on local or global sequence features) and musical scene analysis (requiring detection of a familiar tune within polyphonic harmony). Performance on these tests was referenced to generic auditory (timbral) deviance detection and recognition of familiar tunes and adjusted for general auditory working memory performance. Relative to healthy controls, patients with AD and LPA had group-level deficits of global pitch (melody contour) processing while patients with PNFA as a group had deficits of local (interval) as well as global pitch processing. There was substantial individual variation within syndromic groups. Taking working memory performance into account, no specific deficits of musical temporal processing, timbre processing, musical scene analysis, or tune recognition were identified. The findings suggest that particular aspects of music perception such as pitch pattern analysis may open a window on the processing of information streams in major dementia syndromes. The potential selectivity of musical deficits for particular dementia syndromes and particular dimensions of processing warrants further systematic investigation.

Temporal processing in schizophrenia: effects of task-difficulty on behavioral discrimination and neuronal responses

Deficits in temporal judgment in schizophrenia have been observed in behavioral and electrophysiological studies for years. The functional neuroanatomy of temporal judgment in schizophrenia is, however, poorly understood. Recent neurophysiological research suggests that timing deficits in this population may not be widespread across all timing tasks, but specifically associated with high levels of difficulty. We evaluated differences between individuals with schizophrenia (N=16) and healthy subjects (N=18) during a temporal discrimination task at two levels of difficulty. Subjects were studied with functional magnetic resonance imaging (fMRI) at 3T while discriminating tone durations. Behaviorally, the schizophrenia group performed worse than the control group at both levels of difficulty. Similarly, group differences in patterns of brain activation were observed across both difficulty conditions. In the easy condition, individuals with schizophrenia showed less activation in the supplementary motor area and insula/opercula, regions known to be involved in temporal processing. These group differences increased in the difficult condition. In addition, the striatum was less active in individuals with schizophrenia in the difficult condition. Comparing the difficult to easy conditions revealed robust differences in the bilateral striatum and the insula/opercula, suggesting that the striatum plays a key role in temporal processing deficits in schizophrenia, especially under difficult conditions. These observations suggest that temporal judgment deficits reflect widespread neuroanatomical network involvement in schizophrenia, some of which are not directly related to task difficulty. These findings shed light on disparate findings in the timing literature regarding the role of task difficulty in temporal judgment deficits in schizophrenia.

Effect of task difficulty on the functional anatomy of temporal processing

Temporal processing underlies many aspects of human perception, performance and cognition. The present study used fMRI to examine the functional neuroanatomy of a temporal discrimination task and to address two questions highlighted by previous studies: (1) the effect of task difficulty on neuronal activation and (2) the involvement of the dorsolateral prefrontal cortex (DLPFC) in timing. Twenty healthy subjects were scanned while either judging whether the second in a pair of tones was shorter or longer in duration than the standard tone or simply responding to the presentation of two identical tones as a control condition. Two levels of difficulty were studied. Activation during the less difficult condition was observed only in the cerebellum and superior temporal gyrus. As difficulty increased, additional activation of the supplementary motor area, insula/operculum, DLPFC, thalamus and striatum was observed. These results suggest the cerebellum plays a critical role in timing, particularly in gross temporal discrimination. These results also suggest that recruitment of frontal and striatal regions during timing tasks is load-dependent. Additionally, robust activation of the dorsolateral prefrontal cortex under conditions of minimal working memory involvement supports the specific involvement of this region in temporal processing rather than a more general involvement in working memory.

Song and speech: Brain regions involved with perception and covert production

This 3-T fMRI study investigates brain regions similarly and differentially involved with listening and covert production of singing relative to speech. Given the greater use of auditory-motor self-monitoring and imagery with respect to consonance in singing, brain regions involved with these processes are predicted to be differentially active for singing more than for speech. The stimuli consisted of six Japanese songs. A block design was employed in which the tasks for the subject were to listen passively to singing of the song lyrics, passively listen to speaking of the song lyrics, covertly sing the song lyrics visually presented, covertly speak the song lyrics visually presented, and to rest. The conjunction of passive listening and covert production tasks used in this study allow for general neural processes underlying both perception and production to be discerned that are not exclusively a result of stimulus induced auditory processing nor to low level articulatory motor control. Brain regions involved with both perception and production for singing as well as speech were found to include the left planum temporale/superior temporal parietal region, as well as left and right premotor cortex, lateral aspect of the VI lobule of posterior cerebellum, anterior superior temporal gyrus, and planum polare. Greater activity for the singing over the speech condition for both the listening and covert production tasks was found in the right planum temporale. Greater activity in brain regions involved with consonance, orbitofrontal cortex (listening task), subcallosal cingulate (covert production task) were also present for singing over speech. The results are consistent with the PT mediating representational transformation across auditory and motor domains in response to consonance for singing over that of speech. Hemispheric laterality was assessed by paired t tests between active voxels in the contrast of interest relative to the left-right flipped contrast of interest calculated from images normalized to the left-right reflected template. Consistent with some hypotheses regarding hemispheric specialization, a pattern of differential laterality for speech over singing (both covert production and listening tasks) occurs in the left temporal lobe, whereas, singing over speech (listening task only) occurs in right temporal lobe.

Investigating the neural basis of the auditory continuity illusion

In this study, we investigated one type of auditory perceptual grouping phenomena--the auditory continuity illusion (also called temporal induction). We employed a previously developed, neurobiologically realistic, large-scale neural network model of the auditory processing pathway in the cortex, ranging from the primary auditory cortex to the prefrontal cortex, and simulated temporal induction without changing any model parameters. The model processes tonal contour stimuli, composed of combinations of upward and downward FM sweeps and tones, in a delayed match-to-sample task. The local electrical activities of the neuronal units of the model simulated accurately the experimentally observed electrophysiological data, where available, and the model's simulated BOLD-fMRI data were quantitatively matched with experimental fMRI data. In the present simulations, intact stimuli were matched with fragmented versions (i.e., with inserted silent gaps). The ability of the model to match fragmented stimuli declined as the duration of the gaps increased. However, when simulated broadband noise was inserted into these gaps, the matching response was restored, indicating that a continuous stimulus was perceived. The electrical activities of the neuronal units of the model agreed with electrophysiological data, and the behavioral activity of the model matched human behavioral data. In the model, the predominant mechanism implementing temporal induction is the divergence of the feedforward connections along the auditory processing pathway in the temporal cortex. These simulation results not only attest to the robustness of the model, but further predict the primary role of the anatomical connectivity of the auditory processing areas in mediating the continuity illusion.

On the benefits of not trying: brain activity and connectivity reflecting the interactions of explicit and implicit sequence learning

Under certain circumstances, implicit, automatic learning may be attenuated by explicit memory processes. We explored the brain basis of this phenomenon in a functional magnetic resonance imaging (fMRI) study of motor sequence learning. Using a factorial design that crossed subjective intention to learn (explicit versus implicit) with sequence difficulty (a standard versus a more complex alternating sequence), we show that explicit attempts to learn the difficult sequence produce a failure of implicit learning and, in a follow-up behavioural experiment, that this failure represents a suppression of learning itself rather than of the expression of learning. This suppression is associated with sustained right frontal activation and attenuation of learning-related changes in the medial temporal lobe and the thalamus. Furthermore, this condition is characterized by a reversal of the fronto-thalamic connectivity observed with unimpaired implicit learning. The findings demonstrate a neural basis for a well-known behavioural effect: the deleterious impact of an explicit search upon implicit learning.

The intraparietal sulcus and perceptual organization

The structuring of the sensory scene (perceptual organization) profoundly affects what we perceive, and is of increasing clinical interest. In both vision and audition, many cues have been identified that influence perceptual organization, but only a little is known about its neural basis. Previous studies have suggested that auditory cortex may play a role in auditory perceptual organization (also called auditory stream segregation). However, these studies were limited in that they just examined auditory cortex and that the stimuli they used to generate different organizations had different physical characteristics, which per se may have led to the differences in neural response. In the current study, functional magnetic resonance imaging was used to test for an effect of perceptual organization across the whole brain. To avoid confounding physical changes to the stimuli with differences in perceptual organization, we exploited an ambiguous auditory figure that is sometimes perceived as a single auditory stream and sometimes as two streams. We found that regions in the intraparietal sulcus (IPS ) showed greater activity when 2 streams were perceived rather than 1. The specific involvement of this region in perceptual organization is exciting, as there is a growing literature that suggests a role for the IPS in binding in vision, touch, and cross-modally. This evidence is discussed, and a general role proposed for regions of the IPS in structuring sensory input.

Deficient auditory interhemispheric transfer in patients with PAX6 mutations

PAX6 mutations are associated with absence/hypoplasia of the anterior commissure and reduction in the callosal area in humans. Both of these structures contain auditory interhemispheric fibers. The aim of this study was to characterize central auditory function in patients with a PAX6 mutation. We conducted central auditory tests (dichotic speech, pattern, and gaps in noise tests) on eight subjects with a PAX6 mutation and eight age- and sex-matched controls. Brain magnetic resonance imaging showed absent/hypoplastic anterior commissure in six and a hypoplastic corpus callosum in three PAX6 subjects. The control group gave normal central auditory tests results. All the PAX6 subjects gave abnormal results in at least two tests that require interhemispheric transfer, and all but one gave normal results in a test not requiring interhemispheric transfer. The left ear scores in the dichotic speech tests was significantly lower in the PAX6 than in the control group. These results are consistent with deficient auditory interhemispheric transfer in patients with a PAX6 mutation, which may be attributable to structural and/or functional abnormalities of the anterior commisure and corpus callosum, although the exact contribution of these two formations to our findings remains unclear. Our unique findings broaden the possible functions of PAX6 to include neurodevelopmental roles in higher order auditory processing.