Tommi Raij

Task-modulated “what” and “where” pathways in human auditory cortex

Human neuroimaging studies suggest that localization and identification of relevant auditory objects are accomplished via parallel parietal-to-lateral-prefrontal “where” and anterior-temporal-to-inferior-frontal “what” pathways, respectively. Using combined hemodynamic (functional MRI) and electromagnetic (magnetoencephalography) measurements, we investigated whether such dual pathways exist already in the human nonprimary auditory cortex, as suggested by animal models, and whether selective attention facilitates sound localization and identification by modulating these pathways in a feature-specific fashion. We found a double dissociation in response adaptation to sound pairs with phonetic vs. spatial sound changes, demonstrating that the human nonprimary auditory cortex indeed processes speech-sound identity and location in parallel anterior “what” (in anterolateral Heschl’s gyrus, anterior superior temporal gyrus, and posterior planum polare) and posterior “where” (in planum temporale and posterior superior temporal gyrus) pathways as early as ≈70–150 ms from stimulus onset. Our data further show that the “where” pathway is activated ≈30 ms earlier than the “what” pathway, possibly enabling the brain to use top-down spatial information in auditory object perception. Notably, selectively attending to phonetic content modulated response adaptation in the “what” pathway, whereas attending to sound location produced analogous effects in the “where” pathway. This finding suggests that selective-attention effects are feature-specific in the human nonprimary auditory cortex and that they arise from enhanced tuning of receptive fields of task-relevant neuronal populations.

Timing of human cortical functions during cognition: role of MEG

Understanding of sensory and cognitive brain processes requires information about activation timing within and between different brain sites. Such data can be obtained by magnetoencephalography (MEG) that tracks cortical activation sequences with a millisecond temporal accuracy. MEG is gaining a well-established role in human neuroscience, complementing with its excellent temporal resolution the spatially more focused brain imaging methods. As examples of MEGs role in cognitive neuroscience, we discuss time windows related to cortical processing of sensory and multisensory stimuli, effects of the subjects own voice on the activity of their auditory cortex, timing of brain activation in reading, and cortical dynamics of the human mirror-neuron system activated when the subject views another persons movements.

Short-term plasticity in auditory cognition.

Converging lines of evidence suggest that auditory system short-term plasticity can enable several perceptual and cognitive functions that have been previously considered as relatively distinct phenomena. Here we review recent findings suggesting that auditory stimulation, auditory selective attention and cross-modal effects of visual stimulation each cause transient excitatory and (surround) inhibitory modulations in the auditory cortex. These modulations might adaptively tune hierarchically organized sound feature maps of the auditory cortex (e.g. tonotopy), thus filtering relevant sounds during rapidly changing environmental and task demands. This could support auditory sensory memory, pre-attentive detection of sound novelty, enhanced perception during selective attention, influence of visual processing on auditory perception and longer-term plastic changes associated with perceptual learning.

Human auditory cortex is activated by omissions of auditory stimuli

Cortical signals associated with infrequent tone omissions were recorded from 9 healthy adults with a whole-head 122 channel neuromagnetometer. The stimulus sequence consisted of monaural (left or right) 50-ms 1-kHz tones repeated every 0.2 or 0.5 s, with 7% of the tones randomly omitted. Tones elicited typical responses in the supratemporal auditory cortices. Omissions evoked strong responses over temporal and frontal areas, independently of the side of stimulation, with peak amplitudes at 145-195 ms. Response amplitudes were 60% weaker when the subject was not attending to the stimuli. Omission responses originated in supratemporal auditory cortices bilaterally, indicating that auditory cortex plays an important role in the brains modelling of temporal characteristics of the auditory environment. Additional activity was observed in the posterolateral frontal cortex and in the superior temporal sulcus, more often in the right than in the left hemisphere.

Attention-driven auditory cortex short-term plasticity helps segregate relevant sounds from noise

How can we concentrate on relevant sounds in noisy environments? A “gain model” suggests that auditory attention simply amplifies relevant and suppresses irrelevant afferent inputs. However, it is unclear whether this suffices when attended and ignored features overlap to stimulate the same neuronal receptive fields. A “tuning model” suggests that, in addition to gain, attention modulates feature selectivity of auditory neurons. We recorded magnetoencephalography, EEG, and functional MRI (fMRI) while subjects attended to tones delivered to one ear and ignored opposite-ear inputs. The attended ear was switched every 30 s to quantify how quickly the effects evolve. To produce overlapping inputs, the tones were presented alone vs. during white-noise masking notch-filtered ±1/6 octaves around the tone center frequencies. Amplitude modulation (39 vs. 41 Hz in opposite ears) was applied for “frequency tagging” of attention effects on maskers. Noise masking reduced early (50–150 ms; N1) auditory responses to unattended tones. In support of the tuning model, selective attention canceled out this attenuating effect but did not modulate the gain of 50–150 ms activity to nonmasked tones or steady-state responses to the maskers themselves. These tuning effects originated at nonprimary auditory cortices, purportedly occupied by neurons that, without attention, have wider frequency tuning than ±1/6 octaves. The attentional tuning evolved rapidly, during the first few seconds after attention switching, and correlated with behavioral discrimination performance. In conclusion, a simple gain model alone cannot explain auditory selective attention. In nonprimary auditory cortices, attention-driven short-term plasticity retunes neurons to segregate relevant sounds from noise.

Onset timing of cross‐sensory activations and multisensory interactions in auditory and visual sensory cortices

Here we report early cross‐sensory activations and audiovisual interactions at the visual and auditory cortices using magnetoencephalography (MEG) to obtain accurate timing information. Data from an identical fMRI experiment were employed to support MEG source localization results. Simple auditory and visual stimuli (300‐ms noise bursts and checkerboards) were presented to seven healthy humans. MEG source analysis suggested generators in the auditory and visual sensory cortices for both within‐modality and cross‐sensory activations. fMRI cross‐sensory activations were strong in the visual but almost absent in the auditory cortex; this discrepancy with MEG possibly reflects the influence of acoustical scanner noise in fMRI. In the primary auditory cortices (Heschl’s gyrus) the onset of activity to auditory stimuli was observed at 23 ms in both hemispheres, and to visual stimuli at 82 ms in the left and at 75 ms in the right hemisphere. In the primary visual cortex (Calcarine fissure) the activations to visual stimuli started at 43 ms and to auditory stimuli at 53 ms. Cross‐sensory activations thus started later than sensory‐specific activations, by 55 ms in the auditory cortex and by 10 ms in the visual cortex, suggesting that the origins of the cross‐sensory activations may be in the primary sensory cortices of the opposite modality, with conduction delays (from one sensory cortex to another) of 30–35 ms. Audiovisual interactions started at 85 ms in the left auditory, 80 ms in the right auditory and 74 ms in the visual cortex, i.e., 3–21 ms after inputs from the two modalities converged.

Left-hemisphere dominance for processing of vowels : a whole-scalp neuromagnetic study

Brain activation of 11 healthy right-handed subjects was studied with magnetoencephalography to estimate individual hemispheric dominance for speech sounds. The auditory stimuli comprised binaurally presented Finnish vowels, tones, and piano notes in groups of two or four stimuli. The subjects were required to detect whether the first and the last item in a group were the same. In the left hemisphere, vowels evoked significantly stronger (37-79%) responses than notes and tones, whereas in the right hemisphere the responses to different stimuli did not differ significantly. Specifically, in the two-stimulus task, all 11 subjects showed left-hemisphere dominance in the vowel vs tone comparison. This simple paradigm may be helpful in non-invasive evaluation of language lateralization.

Primary and multisensory cortical activity is correlated with audiovisual percepts

Incongruent auditory and visual stimuli can elicit audiovisual illusions such as the McGurk effect where visual /ka/ and auditory /pa/ fuse into another percept such as/ta/. In the present study, human brain activity was measured with adaptation functional magnetic resonance imaging to investigate which brain areas support such audiovisual illusions. Subjects viewed trains of four movies beginning with three congruent /pa/ stimuli to induce adaptation. The fourth stimulus could be (i) another congruent /pa/, (ii) a congruent /ka/, (iii) an incongruent stimulus that evokes the McGurk effect in susceptible individuals (lips /ka/ voice /pa/), or (iv) the converse combination that does not cause the McGurk effect (lips /pa/ voice/ ka/). This paradigm was predicted to show increased release from adaptation (i.e. stronger brain activation) when the fourth movie and the related percept was increasingly different from the three previous movies. A stimulus change in either the auditory or the visual stimulus from /pa/ to /ka/ (iii, iv) produced within‐modality and cross‐modal responses in primary auditory and visual areas. A greater release from adaptation was observed for incongruent non‐McGurk (iv) compared to incongruent McGurk (iii) trials. A network including the primary auditory and visual cortices, nonprimary auditory cortex, and several multisensory areas (superior temporal sulcus, intraparietal sulcus, insula, and pre‐central cortex) showed a correlation between perceiving the McGurk effect and the fMRI signal, suggesting that these areas support the audiovisual illusion. Hum Brain Mapp, 2010.

Mind's ear in a musician: Where and when in the brain?

The temporospatial pattern of brain activity during auditory imagery was studied using magnetoencephalography. Trained musicians were presented with visual notes and instructed to imagine the corresponding sounds. Brain activity specific to the auditory imagery task was observed, first as enhanced activity of left and right occipital areas (average onset 120-150 ms after the onset of the visual stimulus) and then spreading to the midline parietal cortex (precuneus) and to such extraoccipital areas that were not activated during the visual control condition (e.g., the left temporal auditory association cortex and the left and right premotor cortices). The latest activations, with average onset latencies of 270-400 ms clearly separate from the earliest ones, occurred in the left sensorimotor cortex and the right inferotemporal visual association cortex. These data imply a complex temporospatial activation sequence of multiple cortical areas when musicians recall firmly established audiovisual associations.

Transcranial magnetic stimulation of the brain: guidelines for pain treatment research

Abstract Recognizing that electrically stimulating the motor cortex could relieve chronic pain sparked development of noninvasive technologies. In transcranial magnetic stimulation (TMS), electromagnetic coils held against the scalp influence underlying cortical firing. Multiday repetitive transcranial magnetic stimulation (rTMS) can induce long-lasting, potentially therapeutic brain plasticity. Nearby ferromagnetic or electronic implants are contraindications. Adverse effects are minimal, primarily headaches. Single provoked seizures are very rare. Transcranial magnetic stimulation devices are marketed for depression and migraine in the United States and for various indications elsewhere. Although multiple studies report that high-frequency rTMS of the motor cortex reduces neuropathic pain, their quality has been insufficient to support Food and Drug Administration application. Harvards Radcliffe Institute therefore sponsored a workshop to solicit advice from experts in TMS, pain research, and clinical trials. They recommended that researchers standardize and document all TMS parameters and improve strategies for sham and double blinding. Subjects should have common well-characterized pain conditions amenable to motor cortex rTMS and studies should be adequately powered. They recommended standardized assessment tools (eg, NIHs PROMIS) plus validated condition-specific instruments and consensus-recommended metrics (eg, IMMPACT). Outcomes should include pain intensity and qualities, patient and clinician impression of change, and proportions achieving 30% and 50% pain relief. Secondary outcomes could include function, mood, sleep, and/or quality of life. Minimum required elements include sample sources, sizes, and demographics, recruitment methods, inclusion and exclusion criteria, baseline and posttreatment means and SD, adverse effects, safety concerns, discontinuations, and medication-usage records. Outcomes should be monitored for at least 3 months after initiation with prespecified statistical analyses. Multigroup collaborations or registry studies may be needed for pivotal trials.