A dynamical pattern recognition model of γ activity in auditory cortex.

This paper describes a dynamical process which serves both as a model of temporal pattern recognition in the brain and as a forward model of neuroimaging data. This process is considered at two separate levels of analysis: the algorithmic and implementation levels. At an algorithmic level, recognition is based on the use of Occurrence Time features. Using a speech digit database we show that for noisy recognition environments, these features rival standard cepstral coefficient features. At an implementation level, the model is defined using a Weakly Coupled Oscillator (WCO) framework and uses a transient synchronization mechanism to signal a recognition event. In a second set of experiments, we use the strength of the synchronization event to predict the high gamma (75-150 Hz) activity produced by the brain in response to word versus non-word stimuli. Quantitative model fits allow us to make inferences about parameters governing pattern recognition dynamics in the brain.

Lesion sites that predict the ability to gesture how an object is used.

We used a two stage procedure to predict which stroke patients would have chronic difficulties gesturing how to use an object when object recognition and hand movements were intact. First, we searched our PLORAS database by behavior and identified 5 patients who had chronic difficulty gesturing object use but no difficulty recognising objects, comprehending words or moving their hands. High definition lesion analyses showed that all 5 patients had damage to the white matter underlying the left ventral supramarginal gyrus, (A) close to the cortex, (B) deep towards the midline and (C) extending into the temporal lobe. In addition, 2 patients had damage to (D) the left posterior middle temporal cortex, and 3 patients had damage to (E) the left dorsal supramarginal gyrus and (F) the left premotor cortex. Second, we searched our database by lesion location for patients who had damage to any part of regions ABCDEF. The incidence of gesturing difficulties was higher in patients with damage to ABCD (7/9), ABCE (7/10) or ABCDE (10/13) than ABCF (7/13), ABC (8/16) or partial damage to ABCF (6/32). Thus behaviour was best predicted by the combination of regions that were damaged (a "network-lesion") rather than on the basis of each region alone or overall lesion size. Our results identify which parts of the temporal and parietal lobes impair the ability to gesture object use and which parts need to be intact to support it after damage. Our methods provide a framework for future studies aiming to predict the consequences of brain damage.

Changing meaning causes coupling changes within higher levels of the cortical hierarchy.

Processing of speech and nonspeech sounds occurs bilaterally within primary auditory cortex and surrounding regions of the superior temporal gyrus; however, the manner in which these regions interact during speech and nonspeech processing is not well understood. Here, we investigate the underlying neuronal architecture of the auditory system with magnetoencephalography and a mismatch paradigm. We used a spoken word as a repeating "standard" and periodically introduced 3 "oddball" stimuli that differed in the frequency spectrum of the word's vowel. The closest deviant was perceived as the same vowel as the standard, whereas the other 2 deviants were perceived as belonging to different vowel categories. The neuronal responses to these vowel stimuli were compared with responses elicited by perceptually matched tone stimuli under the same paradigm. For both speech and tones, deviant stimuli induced coupling changes within the same bilateral temporal lobe system. However, vowel oddball effects increased coupling within the left posterior superior temporal gyrus, whereas perceptually equivalent nonspeech oddball effects increased coupling within the right primary auditory cortex. Thus, we show a dissociation in neuronal interactions, occurring at both different hierarchal levels of the auditory system (superior temporal versus primary auditory cortex) and in different hemispheres (left versus right). This hierarchical specificity depends on whether auditory stimuli are embedded in a perceptual context (i.e., a word). Furthermore, our lateralization results suggest left hemisphere specificity for the processing of phonological stimuli, regardless of their elemental (i.e., spectrotemporal) characteristics.