Maryam Soltani

High Gamma Power Is Phase-Locked to Theta Oscillations in Human Neocortex

We observed robust coupling between the high- and low-frequency bands of ongoing electrical activity in the human brain. In particular, the phase of the low-frequency theta (4 to 8 hertz) rhythm modulates power in the high gamma (80 to 150 hertz) band of the electrocorticogram, with stronger modulation occurring at higher theta amplitudes. Furthermore, different behavioral tasks evoke distinct patterns of theta/high gamma coupling across the cortex. The results indicate that transient coupling between low- and high-frequency brain rhythms coordinates activity in distributed cortical areas, providing a mechanism for effective communication during cognitive processing in humans.

Spatiotemporal dynamics of word processing in the human brain

We examined the spatiotemporal dynamics of word processing by recording the electrocorticogram (ECoG) from the lateral frontotemporal cortex of neurosurgical patients chronically implanted with subdural electrode grids. Subjects engaged in a target detection task where proper names served as infrequent targets embedded in a stream of task-irrelevant verbs and nonwords. Verbs described actions related to the hand (e.g, throw) or mouth (e.g., blow), while unintelligible nonwords were sounds which matched the verbs in duration, intensity, temporal modulation, and power spectrum. Complex oscillatory dynamics were observed in the delta, theta, alpha, beta, low, and high gamma (HG) bands in response to presentation of all stimulus types. HG activity (80–200 Hz) in the ECoG tracked the spatiotemporal dynamics of word processing and identified a network of cortical structures involved in early word processing. HG was used to determine the relative onset, peak, and offset times of local cortical activation during word processing. Listening to verbs compared to nonwords sequentially activates first the posterior superior temporal gyrus (post-STG), then the middle superior temporal gyrus (mid-STG), followed by the superior temporal sulcus (STS). We also observed strong phase-locking between pairs of electrodes in the theta band, with weaker phase-locking occurring in the delta, alpha, and beta frequency ranges. These results provide details on the first few hundred milliseconds of the spatiotemporal evolution of cortical activity during word processing and provide evidence consistent with the hypothesis that an oscillatory hierarchy coordinates the flow of information between distinct cortical regions during goal-directed behavior.

Recognition memory for faces: When familiarity supports associative recognition judgments

Recognition memory for single items can be dissociated from recognition memory for the associations between items. For example, recognition tests for single words produce curvilinear receiver operating characteristics (ROCs), but associative recognition tests for word pairs produce linear ROCs. These dissociations are consistent with dual-process theories of recognition and suggest that associative recognition relies on recollection but that item recognition relies on a combination of recollection and assessments of familiarity. In the present study, we examined associative recognition ROCs for facial stimuli by manipulating the central and external features, in order to determine whether linear ROCs would be observed for stimuli other than arbitrary word pairs. When the faces were presented upright, familiarity estimates were significantly above zero, and the associative ROCs were curvilinear, suggesting that familiarity contributed to associative judgments. However, presenting the faces upside down effectively eliminated the contribution of familiarity to associative recognition, and the ROCs were linear. The results suggest that familiarity can support associative recognition judgments, if the associated components are encoded as a coherent gestalt, as in upright faces.

Perceptual Load and Visuocortical Processing: Event-Related Potentials Reveal Sensory-Level Selection

Behavioral evidence suggests that the processing of parafoveal stimuli decreases as the perceptual demands of a task at fixation increase. However, it remains unclear whether or not this effect of perceptual load occurs during initial sensory-level processing at early stages of visuocortical analysis. Using event-related potential measures, we found that increasing the perceptual load of foveal targets led to a significant decrease in the sensory-evoked response to parafoveal stimuli. Moreover, these effects were observed using two different operational definitions of perceptual load. This result indicates that perceptual load affects the flow of information during the initial stages of visuocortical processing.

Comparison of Time–Frequency Responses and the Event-Related Potential to Auditory Speech Stimuli in Human Cortex

We recorded the electrocorticogram directly from the exposed cortical surface of awake neurosurgical patients during the presentation of auditory syllable stimuli. All patients were unanesthetized as part of a language-mapping procedure for subsequent left-hemisphere tumor resection. Time-frequency analyses showed significant high-gamma (gammahigh: 70-160 Hz) responses from the left superior temporal gyrus, but no reliable response from the left inferior frontal gyrus. Alpha suppression (alpha: 7-14 Hz) and event-related potential responses exhibited a more widespread topography. Across electrodes, the alpha suppression from 200 to 450 ms correlated with the preceding (50-200 ms) gammahigh increase. The results are discussed in terms of the different physiological origins of these electrocortical signals.

Emotionally arousing stimuli compete for attention with left hemispace.

Rapid interaction of the emotional and attentional networks is critical for adaptive behavior. Here, we examined the effects of emotional stimulation on hemifield attention allocation using event-related potential and behavioral measures. Participants performed a visual-discrimination task on nonemotional targets presented randomly in the left or right hemifield. A brief task-irrelevant emotional (pleasant or unpleasant; 150-ms duration) or neutral picture was presented centrally 350 ms before the next target (150-ms duration). Unpleasant stimuli interfered with the left visual field attention capacity, slowing behavioral responses to attended left field stimuli. In keeping with the behavioral data, event-related potential responses to nonemotional attended left field stimuli were reduced over the right parietal regions when preceded by an unpleasant event. The results provide electrophysiological and behavioral evidence that unpleasant, emotionally arousing stimuli interfere with the right hemisphere-dependent attention capacity.

Prefrontal cortex lesions impair object-spatial integration.

How and where object and spatial information are perceptually integrated in the brain is a central question in visual cognition. Single-unit physiology, scalp EEG, and fMRI research suggests that the prefrontal cortex (PFC) is a critical locus for object-spatial integration. To test the causal participation of the PFC in an object-spatial integration network, we studied ten patients with unilateral PFC damage performing a lateralized object-spatial integration task. Consistent with single-unit and neuroimaging studies, we found that PFC lesions result in a significant behavioral impairment in object-spatial integration. Furthermore, by manipulating inter-hemispheric transfer of object-spatial information, we found that masking of visual transfer impairs performance in the contralesional visual field in the PFC patients. Our results provide the first evidence that the PFC plays a key, causal role in an object-spatial integration network. Patient performance is also discussed within the context of compensation by the non-lesioned PFC.

When You Go

You know something about me But I know more about you Than I do about many friends So when you go I miss you We have laughed and cried together Over the years Just like old friends do In sickness and in health Formed a bond Broken only by death I hate to see you go You have added so much to my life More than you will ever know I taught you about your health You taught me how to live And die With grace I am a better doctor A better person For having known you If you only knew The secret tears I cry when you go Tears of sadness And of joy We had such good times together You are relieved of your suffering But I still miss you When you go * Maryam Soltani msoltani@ucsd.edu

Want Change Not Coins

I walked into the patient waiting room and called her name, a young woman in her early 20s. She stood and walked towards me, her eyes meeting mine fleetingly. In the exam room, I asked her, “What brings you in to see me?” She said, “I hear voices.” During the course of our interview, I noticed her exaggerated mannerisms: initially soft-spoken with little eye contact, she shifted to yelling and crying, “The voices are driving me crazy!” She covered her ears and sat in a fetal position, rocking back and forth in the chair and talking to herself. She grew up in shelters and defying the safety that shelter connotes, recounted a traumatic past. Her dramatic behavior was not psychotic. Her thinking was logical and sequential. Accustomed to being ignored and neglected, I think she learned to be dramatic to get attention. She wanted me to understand that she no longer wanted to be a mother living on the streets with a fiancé and young child. After interviewing her, I spoke with my attending. When I returned to the exam room with my attending, her behavior became more histrionic; she stopped answering questions and talked to herself. After my attending and I told her about our plan, she became relaxed, spoke to us, and expressed gratitude. The image represents the homeless population that our medical clinic serves in San Diego County. Our patients have survived unimaginable trauma in “shelters” and on the streets. People “want” to be homeless is a misconception. We learn from the homeless that many want change, but find that, once homeless, it is difficult to find housing and employment. How can a person present to a job interview after sleeping on the concrete and wearing unwashed clothing and unbathed? Who * Maryam Soltani msoltani@ucsd.edu

No Place to Call Home

Ayoung boy stands behind a chain-linked fence wondering what his future holds. He reflects on the days he used to run around the open field playing soccer with his friends. He then remembers his father’s screams as he was beaten and tortured because of his political beliefs. He remembers hiding in a bathtub with his mother, father, and sister hoping that they could avoid being found and tortured. Now he sits behind a fence in a refugee camp, torn from his homeland, displaced to a foreign land where he does not speak the language and is expected to assimilate into a culture vastly different from his own. Terrified, he awaits this transition and wonders what will become of him, his family, and friends. Will they come with him? Will they be captured, imprisoned, and tortured? Will anyone ever be the same? According to Amnesty International, refugees are people who fled from their home country to a different country in order to escape conflict or persecution and are either unwilling or unable to return to their home country safely because of their race, religion, nationality, political opinion, and/or membership in a particular social group [1]. Asylum seekers are persons who seek international protection but whose claims have not been definitively evaluated by the country they were submitted to [1]. Once the asylum * Maryam Soltani msoltani@ucsd.edu