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1.  Hemicraniectomy: A New Model for Human Electrophysiology with High Spatio-Temporal Resolution 
Journal of cognitive neuroscience  2010;22(11):2491-2502.
Human electrophysiological research is generally restricted to scalp electroencephalography (EEG), magnetoencephalography, and intracranial electrophysiology. Here we examine a unique patient cohort that has undergone decompressive hemicraniectomy, a surgical procedure wherein a portion of the calvaria is removed for several months during which time the scalp overlies the brain without intervening bone. We quantify the differences in signals between electrodes over areas with no underlying skull and scalp EEG electrodes over the intact skull in the same subjects. Signals over the hemicraniectomy have enhanced amplitude and greater task-related power at higher frequencies (60–115 Hz) compared to signals over skull. We also provide evidence of a metric for trial-by-trial electromyography/EEG coupling that is effective over the hemicraniectomy but not intact skull at frequencies >60 Hz. Taken together these results provide evidence that the hemicraniectomy model provides a means for studying neural dynamics in humans with enhanced spatial and temporal resolution.
doi:10.1162/jocn.2009.21384
PMCID: PMC2888789  PMID: 19925193
2.  Prefrontal cortex is critical for contextual processing: evidence from brain lesions 
Brain  2009;132(11):3002-3010.
We investigated the role of prefrontal cortex (PFC) in local contextual processing using a combined event-related potentials and lesion approach. Local context was defined as the occurrence of a short predictive series of visual stimuli occurring before delivery of a target event. Targets were preceded by either randomized sequences of standards or by sequences including a three-stimulus predictive sequence signalling the occurrence of a subsequent target event. PFC lesioned patients were impaired in their ability to use local contextual information. The response time for controls revealed a larger benefit for predictable targets than for random targets relative to PFC patients. PFC patients had reduced amplitude of a context-dependent positivity and failed to generate the expected P3b latency shift between predictive and non-predictive targets. These findings show that PFC patients are unable to utilize predictive local context to guide behaviour, providing evidence for a critical role of PFC in local contextual processing.
doi:10.1093/brain/awp230
PMCID: PMC2768662  PMID: 19713281
context; prefrontal cortex; P3b; EEG; context positivity
3.  No Disillusions in Auditory Extinction: Perceiving a Melody Comprised of Unperceived Notes 
The formation of coherent percepts requires grouping together spatio-temporally disparate sensory inputs. Two major questions arise: (1) is awareness necessary for this process; and (2) can non-conscious elements of the sensory input be grouped into a conscious percept? To address this question, we tested two patients suffering from severe left auditory extinction following right hemisphere damage. In extinction, patients are unaware of the presence of left side stimuli when they are presented simultaneously with right side stimuli. We used the ‘scale illusion’ to test whether extinguished tones on the left can be incorporated into the content of conscious awareness. In the scale illusion, healthy listeners obtain the illusion of distinct melodies, which are the result of grouping of information from both ears into illusory auditory streams. We show that the two patients were susceptible to the scale illusion while being consciously unaware of the stimuli presented on their left. This suggests that awareness is not necessary for auditory grouping and non-conscious elements can be incorporated into a conscious percept.
doi:10.3389/neuro.09.015.2007
PMCID: PMC2525977  PMID: 18958228
auditory extinction; unilateral neglect; auditory scene analysis; streaming; scale illusion; implicit processing

Results 1-3 (3)