Massihullah Hamidi

Learn More
BACKGROUND A previous study reported reductions in glial density and glia/neuron ratio in the amygdala of individuals with major depressive disorder (MDD), without a change in neuronal density. It is not known, however, whether this glial loss is due to astrocytes, oligodendrocytes, or microglia. METHODS Tissue samples, equally from the right and left(More)
Understanding the contributions of the prefrontal cortex (PFC) to working memory is central to understanding the neural bases of high-level cognition. One question that remains controversial is whether the same areas of the dorsolateral PFC (dlPFC) that participate in the manipulation of information in working memory also contribute to its short-term(More)
A governing assumption about repetitive transcranial magnetic stimulation (rTMS) has been that it interferes with task-related neuronal activity - in effect, by "injecting noise" into the brain - and thereby disrupts behavior. Recent reports of rTMS-produced behavioral enhancement, however, call this assumption into question. We investigated the(More)
Functional neuroimaging studies have produced contradictory data about the extent to which specific regions of the frontal and the posterior parietal cortices contribute to the retention of information in spatial working memory. We used high frequency repetitive transcranial magnetic stimulation (rTMS) to assess the necessity for the short-term retention of(More)
Verbal working memory (VWM), the ability to maintain and manipulate representations of speech sounds over short periods, is held by some influential models to be independent from the systems responsible for language production and comprehension [e.g., Baddeley, A. D. Working memory, thought, and action. New York, NY: Oxford University Press, 2007]. We(More)
BACKGROUND Many recent studies have used repetitive transcranial magnetic stimulation (rTMS) to study brain-behavior relationships. However, the pulse-to-pulse neural effects of rapid delivery of multiple TMS pulses are unknown largely because of TMS-evoked electrical artifacts limiting recording of brain activity.ObjectiveIn this study, TMS-related(More)
Systems models hold working memory to depend on specialized, domain-specific storage buffers. Here, however, we demonstrate that short-term retention of the identity or location of visually presented stimuli is disrupted by nonvisual secondary tasks performed in the dark-passive listening to nouns or endogenous generation of saccades, respectively. This(More)
A commonly held view is that, when delivered during the performance of a task, repetitive TMS (rTMS) influences behavior by producing transient “virtual lesions” in targeted tissue. However, findings of rTMS-related improvements in performance are difficult to reconcile with this assumption. With regard to the mechanism whereby rTMS influences concurrent(More)
Two million Americans use cocaine on a regular basis. Sixty-nine percent of cocaine in the United States is adulterated with levamisole, a veterinary antihelminthic drug. In 2008, the first cases of levamisole-induced agranulocytosis and vasculopathy associated with adulterated cocaine were reported in the southwestern United States. Since then, reports of(More)
The dorsolateral prefrontal cortex (dlPFC) plays an important role in working memory, including the control of memory-guided response. In this study, with 24 subjects, we used high frequency repetitive transcranial magnetic stimulation (rTMS) to evaluate the role of the dlPFC in memory-guided response to two different types of spatial working memory tasks:(More)