A comparative study of bipolar disorder and attention deficit hyperactivity disorder through the measurement of regional cerebral blood flow

Attention Deficit Hyperactivity Disorder (ADHD) and Bipolar Disorder (BPD) are two common neuropsychological disorders which are often present in a comorbid state. I used the results of cerebral blood flow studies made with Single Photon Emission Computer Tomography (SPECT), Positron Emission Tomography (PET) and Functional Magnetic Resonance Imaging (fMRI), to investigate a possible relationship between ADHD and BPD. The common areas of the brain involved in both BPD and ADHD appears to be the prefrontal cortex in its various components, the basal ganglia and possibly the cerebellum which, especially in the past, has been little studied by researchers in relation to ADHD and BPD. Among the differences the blood flow lateralization, present in BPD in states of altered mood, is evident with left hypoperfusion and right hyperperfusion during depression, the opposite in the case of manic state; in ADHD, the lateralization is less constant and of questionable interpretation. In BPD the involvement of a greater number of brain areas, especially the temporal lobe, is common. I advance the hypothesis that BPD progresses from ADHD secondary to expansion of perturbation in cerebral blood flow.

Effects of acute tryptophan depletion on prefrontal-amygdala connectivity while viewing facial signals of aggression

BACKGROUND

Reduced levels of serotonin (5-HT) within prefrontal cortex (PFC)-amygdala circuits have long been implicated in impulsive aggression. However, whether lowering 5-HT alters the dynamic interplay between the PFC and the amygdala has not been directly tested in humans. It is known that manipulating 5-HT via acute tryptophan depletion (ATD) causes variable effects on brain responses to a variety of emotional stimuli, but it remains unclear whether ATD affects functional connectivity in neural networks involved in processing social signals of aggression (e.g., angry faces).

METHODS

Thirty healthy individuals were enrolled in a randomized, double-blind, placebo-controlled ATD study. On each treatment, brain responses to angry, sad, and neutral faces were measured with functional magnetic resonance imaging. Two methods (psycho-physiological-interaction in a general linear model and dynamic causal modeling) were used to assess the impact of ATD on the functional connectivity between PFC and amygdala.

RESULTS

Data from 19 subjects were available for the final analyses. A whole-brain psycho-physiological-interaction in a general linear model showed that ATD significantly modulated the connectivity between the amygdala and two PFC regions (ventral anterior cingulate cortex and ventrolateral PFC) when processing angry vs. neutral and angry vs. sad but not sad vs. neutral faces. Dynamic causal modeling corroborated and extended these findings by showing that 5-HT depletion reduced the influence of processing angry vs. neutral faces on circuits within PFC and on PFC-amygdala pathways.

CONCLUSIONS

We provide strong support for neurobiological accounts positing that 5-HT significantly influences PFC-amygdala circuits implicated in aggression and other affective behaviors.

Decreased regional cerebral blood flow in medial prefrontal cortex during trauma-unrelated stressful imagery in Vietnam veterans with post-traumatic stress disorder

BACKGROUND

Neuroimaging research has demonstrated medial prefrontal cortex (mPFC) hyporesponsivity and amygdala hyperresponsivity to trauma-related or emotional stimuli in post-traumatic stress disorder (PTSD). Relatively few studies have examined brain responses to the recollection of stressful, but trauma-unrelated, personal events in PTSD. In the current study, we sought to determine whether regional cerebral blood flow (rCBF) abnormalities in mPFC and amygdala in PTSD could be observed during the recollection of trauma-unrelated stressful personal events.

METHOD

Participants were 35 right-handed male combat veterans (MCVs) and female nurse veterans (FNVs) who served in Vietnam: 17 (seven male, 10 female) with current military-related PTSD and 18 (nine male, nine female) with no current or lifetime PTSD. We used positron emission tomography (PET) and script-driven imagery to study rCBF during the recollection of trauma-unrelated stressful versus neutral and traumatic events.

RESULTS

Voxelwise tests revealed significant between-group differences for the trauma-unrelated stressful versus neutral comparison in mPFC, specifically in the anterior cingulate cortex (ACC). Functional region of interest (ROI) analyses demonstrated that this interaction in mPFC represented greater rCBF decreases in the PTSD group during trauma-unrelated stressful imagery relative to neutral imagery compared to the non-PTSD group. No differential amygdala activation was observed between groups or in either group separately.

CONCLUSIONS

Veterans with PTSD, compared to those without PTSD, exhibited decreased rCBF in mPFC during mental imagery of trauma-unrelated stressful personal experiences. Functional neuroanatomical models of PTSD must account for diminished mPFC responses that extend to emotional stimuli, including stressful personal experiences that are not directly related to PTSD.

Synchronous activity of two people's prefrontal cortices during a cooperative task measured by simultaneous near-infrared spectroscopy

The brain activity during cooperation as a form of social process is studied. We investigate the relationship between coinstantaneous brain-activation signals of multiple participants and their cooperative-task performance. A wearable near-infrared spectroscopy (NIRS) system is used for simultaneously measuring the brain activities of two participants. Each pair of participants perform a cooperative task, and their relative changes in cerebral blood are measured with the NIRS system. As for the task, the participants are told to count 10 s in their mind after an auditory cue and press a button. They are also told to adjust the timing of their button presses to make them as synchronized as possible. Certain information, namely, the "intertime interval" between the two button presses of each participant pair and which of the participants was the faster, is fed back to the participants by a beep sound after each trial. When the spatiotemporal covariance between the activation patterns of the prefrontal cortices of each participant is higher, the intertime interval between their button-press times was shorter. This result suggests that the synchronized activation patterns of the two participants' brains are associated with their performance when they interact in a cooperative task.

Interactive effects of DAOA (G72) and catechol-O-methyltransferase on neurophysiology in prefrontal cortex

BACKGROUND

Accumulating evidence indicates that genetic polymorphisms of D-amino acid oxidase activator (DAOA) (M24; rs1421292; T-allele) and catechol-O-methyltransferase (COMT) (Val¹⁵⁸Met; rs4680) likely enhance susceptibility to schizophrenia. Previously, clinical association between DAOA M24 (T-allele) and a functionally inefficient 3-marker COMT haplotype (that included COMT Val¹⁵⁸Met) uncovered epistatic effects on risk for schizophrenia. Therefore, we projected that healthy control subjects with risk genotypes for both DAOA M24 (T/T) and COMT Val¹⁵⁸Met (Val/Val) would produce prefrontal inefficiency, a critical physiological marker of the dorsolateral prefrontal cortex (DLPFC) in schizophrenic patients influenced by both familial and heritable factors.

METHODS

With 3T blood oxygen level dependent functional magnetic resonance imaging data, we analyzed in SPM5 the proposed interaction of DAOA and COMT in 82 healthy volunteers performing an N-back executive working memory paradigm (2-back > 0-back).

RESULTS

As predicted, we detected a functional gene x gene interaction between DAOA and COMT in the DLPFC.

CONCLUSIONS

The neuroimaging findings here of inefficient information processing in the prefrontal cortex seem to echo prior statistical epistasis between risk alleles for DAOA and COMT, albeit within a small sample. These in vivo results suggest that deleterious genotypes for DAOA and COMT might contribute to the pathophysiology of schizophrenia, perhaps through combined glutamatergic and dopaminergic dysregulation.

Elevated BMI is associated with decreased blood flow in the prefrontal cortex using SPECT imaging in healthy adults

Obesity is a risk factor for stroke and neurodegenerative disease. Excess body fat has been linked to impaired glucose metabolism, insulin resistance, and impulsivity and may be a precursor to decline in attention and executive cognitive function. Here, we investigated the effects of high BMI on regional cerebral blood flow (rCBF) using single photon emission computed tomography (SPECT) imaging in healthy subjects. A total of 16 adult men and 20 adult women were recruited from the community between January 2003 and July 2009 as part of a healthy brain study (HBS) conducted at the Amen Clinics, a private medical facility. Participants in the study were screened to exclude medical, neurological, and psychiatric conditions, including substance abuse. Subjects were categorized as normal or overweight according to BMI. Using a two sample t-test, we determined the effects of BMI on rCBF in normal vs. overweight subjects. Subjects were matched for age and gender. Statistical parametric mapping (SPM) revealed a higher BMI in healthy individuals that is associated with decreased rCBF in Broadmann areas 8, 9, 10, 11, 32, and 44, brain regions involved in attention, reasoning, and executive function (P < 0.05, corrected for multiple comparisons). We found that an elevated BMI is associated with decreased rCBF in the prefrontal cortex of a healthy cohort. These results indicate that elevated BMI may be a risk factor for decreased prefrontal cortex function and potentially impaired executive function.

Estrogen shapes dopamine-dependent cognitive processes: implications for women's health

The prefrontal cortex (PFC) is exquisitely sensitive to its neurochemical environment. Minor fluctuations in cortical dopamine (DA) can profoundly alter working memory, a PFC-dependent cognitive function that supports an array of essential human behaviors. Dopamine's action in the PFC follows an inverted U-shaped curve, where an optimal DA level results in maximal function and insufficient or excessive DA impairs PFC function. In animals, 17β-estradiol (the major estrogen in most mammals, referred to henceforth as estradiol) has been shown to enhance DA activity, yet no human study has adequately addressed whether estradiol's impact on cognition occurs by way of modulating specific neurochemical systems. Here we examined the effects of endogenous fluctuations in estradiol on working memory in healthy young women as a function of baseline PFC DA [indexed by catechol-O-methyltransferase (COMT) Val(158)Met genotype and, at a finer scale, COMT enzyme activity]. The results demonstrate that estradiol status impacts working memory function and, crucially, the direction of the effect depends on indices of baseline DA. Moreover, consistent with a DA cortical efficiency hypothesis, functional MRI revealed that inferred optimal DA was associated with reduced PFC activity sustained across task blocks and selectively enhanced PFC activity on trials with the greatest demand for cognitive control. The magnitude of PFC activity during high control trials was predictive of an individual's performance. These findings show that although estrogen, considered in isolation, may have unpredictable effects on cognitive performance, its influence is clarified when considered within a larger neuromodulatory framework. Given the clinical prevalence of dopaminergic drugs, understanding the relationship between estrogen and DA is essential for advancing women's health.

Neural correlates of response inhibition and cigarette smoking in late adolescence

Smoking is usually initiated in adolescence, and is the leading preventable cause of death in the United States. Little is known, however, about the links between smoking and neurobiological function in adolescent smokers. This study aimed to probe prefrontal cortical function in late adolescent smokers, using a response inhibition task, and to assess possible relationships between inhibition-related brain activity, clinical features of smoking behavior, and exposure to cigarette smoking. Participants in this study were otherwise healthy late adolescent smokers (15-21 years of age; n=25), who reported daily smoking for at least the 6 months before testing, and age- and education-matched nonsmokers (16-21 years of age; n=25), who each reported smoking fewer than five cigarettes in their lifetimes. The subjects performed the Stop-signal Task, while undergoing functional magnetic resonance imaging. There were no significant group differences in prefrontal cortical activity during response inhibition, but the Heaviness of Smoking Index, a measure of smoking behavior and dependence, was negatively related to neural function in cortical regions of the smokers. These findings suggest that smoking can modulate prefrontal cortical function. Given the late development of the prefrontal cortex, which continues through adolescence, it is possible that smoking may influence the trajectory of brain development during this critical developmental period.

Dorsolateral prefrontal cortical oxygenation during REM sleep in humans

Previous neuroimaging studies that examined cerebral blood flow during rapid eye movement (REM) sleep have reported inconsistent findings regarding the activity of the dorsolateral prefrontal cortex (DLPFC). Although most previous positron emission tomography (PET) studies failed to detect DLPFC activation during REM sleep, several studies have observed DLPFC activation, possibly reflecting transient prefrontal activities related to REM. More recently, an event-related functional magnetic resonance imaging (fMRI) study observed REM-locked activation of the DLPFC during REM sleep. The present study investigated hemodynamic changes of the DLPFC throughout the REM sleep period in 25 subjects using near-infrared spectroscopy. Continuous monitoring of changes in the hemoglobin (Hb) concentration and tissue oxygenation index (TOI, proportion of oxygenated-Hb to total-Hb) in the bilateral DLPFC was conducted every 0.5s, simultaneously with polysomnographic recordings. Eight of the 25 subjects showed REM sleep, and all indicated a clear increase in both the oxygenated-Hb concentration and TOI from baseline at the occurrence of first REM, relative to prior stage 2 sleep. The results indicate that the appearance of the first REM that occurred just after onset of the REM sleep closely coincides with the activation of the DLPFC, which could play a role in cognitive activities during REM sleep in humans.

Anxiety overrides the blocking effects of high perceptual load on amygdala reactivity to threat-related distractors

Amygdala reactivity to threat-related distractor stimuli can be abolished in perceptually demanding contexts. Premised on the biological imperative to respond swiftly to threat, we demonstrate, however, that when participants are threatened by shock, greater amygdala responses to fearful compared to neutral distractor faces is preserved under conditions of high attentional demand. Lateral prefrontal cortices also showed selective responding to fearful distractor faces under these conditions, suggesting that threat-related distractor stimuli engaged attentional control mechanisms. We conclude that anxiety elicited by looming threat promotes neurocognitive processes that broaden attention and enhance sensitivity to potential danger cues, even when perceptual systems are taxed.

The ergonomics of natural orifice translumenal endoscopic surgery (NOTES) navigation in terms of performance, stress, and cognitive behavior

BACKGROUND

The evolution toward minimally invasive surgery and subsequently to natural orifice translumenal endoscopic surgery (NOTES) poses challenges to the surgeon in terms of increased task complexity requiring greater visuospatial and navigational ability. Neuroergonomics is the study of the brain and behavior at work, and establishing the baseline cortical response for NOTES procedures will help to ascertain whether technological innovation such as navigational aids can alleviate the task-induced cognitive burden. The aims of the current study are to characterize the impact of navigation within a NOTES environment on the subject in terms of (1) performance, (2) stress, (3) prefrontal cortical activity, and (4) how this is influenced by expertise.

METHODS

In all, 29 subjects were assessed for performance, stress response, and prefrontal cortical activity during a NOTES navigational task within a validated NOTES simulator.

RESULTS

Experts performed significantly better than novices (P < .05). Expertise was not a predictor for overall changes in prefrontal cortical activity. The differences between experts and novices were modulated by the location of prefrontal cortical activity, with experts demonstrating more pronounced lateral prefrontal cortical activation compared with novices. Stress was not an independent predictor of changes in prefrontal cortical hemodynamics.

CONCLUSION

This study is the first to characterize the performance, stress, and neurocognitive behavior associated with natural orifice translumenal endoscopic surgery navigation. The results indicate the relevance of visuospatial centers in successful task execution, and they serve as a baseline within the neuroergonomic paradigm for investigating performance-enhancing technology.

The orbitofrontal cortex and its role in the assignment of behavioural significance

Converging evidence suggests a specific role for the orbitofrontal cortex (OFC) in processing of reinforcer value and stimulus hedonicity. However, in a recent study posterior parts of the OFC were also activated in the absence of physical reward or positive reinforcement, namely when affectively neutral stimuli were perceived as salient and required an immediate adjustment of behaviour. This suggests that the OFC may be similarly responsive to different types of behaviourally significant events irrespective of their affective valence or the associated response demands. The present functional neuroimaging study aimed at testing this hypothesis. By systematically varying the exact nature of the behavioural significance of experimental stimuli we were able to directly compare neural responses to significant events that signalled the chance to gain a monetary reward for correct performance with brain activation related to salient, but affectively neutral events that occurred unexpectedly and required a rapid adjustment of behaviour towards these events. The observed commonalities in orbitofrontal activation for different types of significant events, which occurred independent of the hedonic value or the actual response requirements, confirmed the hypothesis that the OFC may be more generally involved in evaluating the behavioural relevance of salient environmental stimuli and is not restricted to the processing of reward and positive incentive value. Our findings thus further underscore the putative role of the OFC in the prioritisation of attentional selection and behavioural control.

Putting the pieces together: the role of dorsolateral prefrontal cortex in relational memory encoding

Results from fMRI have strongly supported the idea that the ventrolateral PFC (VLPFC) contributes to successful memory formation, but the role the dorsolateral PFC (DLPFC) in memory encoding is more controversial. Some findings suggest that the DLPFC is recruited when one is processing relationships between items in working memory, and this processing specifically promotes subsequent memory for these relationships. However, previous studies could not rule out the possibility that DLPFC promotes memory during all elaborative encoding conditions and contributes to memory on all subsequent associative memory tests. To address this question directly, we used fMRI to examine activity during two encoding tasks that prompted participants to encode either relational or item-specific information. On relational trials, participants imagined pairs of items interacting, whereas on item-specific trials, participants imagined the items spatially separated and in different sizes. After scanning, we examined memory for relational information and item-specific information. fMRI results showed that DLPFC activity specifically promoted memory for relational information during relational encoding and not memory for item-specific information during item-specific encoding. In contrast, activity in the VLPFC predicted memory for both relational and item-specific information. The present results are consistent with the idea that the DLPFC specifically contributes to successful memory formation through its role in building relationships among items.

An fMRI study of the prefrontal activity during the performance of a working memory task in premutation carriers of the fragile X mental retardation 1 gene with and without fragile X-associated tremor/ataxia syndrome (FXTAS)

Premutation alleles of the fragile X mental retardation 1 gene (FMR1) are associated with the risk of developing fragile X-associated tremor/ataxia syndrome (FXTAS), a late-onset neurodegenerative disorder that involves neuropsychiatric problems and executive and memory deficits. Although abnormal elevation of FMR1 mRNA has been proposed to underlie these deficits, it remains unknown which brain regions are affected by the disease process of FXTAS and genetic molecular mechanisms associated with the FMR1 premutation. This study used functional magnetic resonance imaging (fMRI) to identify deficient neural substrates responsible for altered executive and memory functions in some FMR1 premutation individuals. We measured fMRI BOLD signals during the performance of verbal working memory from 15 premutation carriers affected by FXTAS (PFX+), 15 premutation carriers unaffected by FXTAS (PFX-), and 12 matched healthy control individuals (HC). We also examined correlation between brain activation and FMR1 molecular variables (CGG repeat size and mRNA levels) in premutation carriers. Compared with HC, PFX+ and PFX- showed reduced activation in the right ventral inferior frontal cortex and left premotor/dorsal inferior frontal cortex. Reduced activation specific to PFX+ was found in the right premotor/dorsal inferior frontal cortex. Regression analysis combining the two premutation groups demonstrated significant negative correlation between the right ventral inferior frontal cortex activity and the levels of FMR1 mRNA after excluding the effect of disease severity of FXTAS. These results indicate altered prefrontal cortex activity that may underline executive and memory deficits affecting some individuals with FMR1 premutation including FXTAS patients.

Left dorsolateral prefrontal cortex dysfunction in medication-naive schizophrenia

Abnormalities in the frontal lobe are considered to be central to the pathology of schizophrenia. Neuroimaging studies indeed report abnormal function of the frontal lobe in schizophrenia patients. However, the nature of these functional abnormalities is unclear, in particular whether they are affected by medication. We therefore investigated whether frontal functioning is already abnormal in first-episode medication-naive schizophrenia, and if so, if this dysfunction is related to symptomatology. Thirty medication-naive male patients with first-episode schizophrenia and 36 matched healthy controls performed a modified working memory task while fMRI data were acquired. During the task, subjects were presented with novel task (NT) and practiced task (PT) memory sets. Compared to controls, patients showed reduced performance during NT and PT. However, both groups performed better during PT, indicating that practice improved performance. Importantly, practice reduced brain activation in both patients and controls, but this effect of practice was significantly smaller in patients compared to controls, specifically in the left dorsolateral prefrontal cortex (DLPFC; p=0.01). The reduced effect of practice on brain activation was related to the severity of negative symptoms and disorganization. These results suggest that DLPFC function is deficient in the early phases of schizophrenia and cannot be attributed to the use of antipsychotics.

The role of ventral medial prefrontal cortex in social decisions: converging evidence from fMRI and frontotemporal lobar degeneration

The ventral medial prefrontal cortex (vmPFC) has been implicated in social and affectively influenced decision-making. Disease in this region may have clinical consequences for social judgments in patients with frontotemporal lobar degeneration (FTLD). To test this hypothesis, regional cortical activation was monitored with fMRI while healthy adults judged the acceptability of brief social scenarios such as cutting into a movie ticket line or going through a red light at 2 AM. The scenarios described: (i) a socially neutral condition, (ii) a variant of each scenario containing a negatively valenced feature, and (iii) a variant containing a positively valenced feature. Results revealed that healthy adults activated vmPFC during judgments of negatively valenced scenarios relative to positive scenarios and neutral scenarios. In a comparative behavioral study, the same social decision-making paradigm was administered to patients with a social disorder due to FTLD. Patients differed significantly from healthy controls, specifically showing less sensitivity to negatively valenced features. Comparative anatomical analysis revealed considerable overlap of vmPFC activation in healthy adults and vmPFC cortical atrophy in FTLD patients. These converging results support the role of vmPFC in social decision-making where potentially negative consequences must be considered.

fMRI BOLD responses to negative stimuli in the prefrontal cortex are dependent on levels of recent negative life stress in major depressive disorder

It is poorly understood how stressors modulate neurobiological mechanisms that may contribute to the heterogeneity of major depressive disorder (MDD). Unmedicated patients diagnosed with MDD (n=15) and individually matched healthy controls (n=15) completed stress questionnaires and were studied with functional magnetic resonance imaging while viewing emotional words. Significant effects of recent negative life stressors, but not early life stress/trauma, were observed on regional blood oxygen level dependent activity during presentation of negative words in patients with MDD. No significant effects of stress on brain activation to negative words were found in controls. In MDD patients, positive correlations were found bilaterally in orbitofrontal areas 11 l/47/12m, which are involved in representing negatively valenced stimuli. Negative correlations were also found in the right ventrolateral prefrontal area 45, subgenual cingulate area 25, and nucleus accumbens, all of which are implicated in the pathophysiology of MDD. Negative memory bias was additionally positively associated with recent negative life stress and negatively associated with subgenual cingulate activation, suggesting a mechanism by which stress may contribute to these abnormalities. The severity of recent negative life stressors is an important modifier of neurobiological and cognitive function in MDD and may help explain heterogeneity in the disorder.

Gender difference in neural response to psychological stress

Gender is an important biological determinant of vulnerability to psychosocial stress. We used perfusion based functional magnetic resonance imaging (fMRI) to measure cerebral blood flow (CBF) responses to mild to moderate stress in 32 healthy people (16 males and 16 females). Psychological stress was elicited using mental arithmetic tasks under varying pressure. Stress in men was associated with CBF increase in the right prefrontal cortex (RPFC) and CBF reduction in the left orbitofrontal cortex (LOrF), a robust response that persisted beyond the stress task period. In contrast, stress in women primarily activated the limbic system, including the ventral striatum, putamen, insula and cingulate cortex. The asymmetric prefrontal activity in males was associated with a physiological index of stress responses-salivary cortisol, whereas the female limbic activation showed a lower degree of correlations with cortisol. Conjunction analyses indicated only a small degree of overlap between the stress networks in men and women at the threshold level of P < 0.01. Increased overlap of stress networks between the two genders was revealed when the threshold for conjunction analyses was relaxed to P < 0.05. Further, machine classification was used to differentiate the central stress responses between the two genders with over 94% accuracy. Our study may represent an initial step in uncovering the neurobiological basis underlying the contrasting health consequences of psychosocial stress in men and women.

Arterial spin-labeled MRI study of migraine attacks treated with rizatriptan

Spin-tag perfusion imaging is an MRI method that quantitatively measures cerebral blood flow. Compared with conventional perfusion techniques, advantages of this arterial spin-labeling (ASL) include repeatability and the avoidance of intravenous contrast administration. In the present study, we performed an analysis of 3T high-field MRI examinations utilizing ASL perfusion during migraine attacks. A 32-year-old male patient was studied in three situations: during migraine attack within 1 h post-onset, 30 min after oral administration of rizatriptan 10 mg, and attack-free period. Normalized ASL images acquired during migraine attack showed significant relative hypoperfusion in the bilateral median thalamic areas including hypothalamus and significant relative hyperperfusion in the frontal cortex compared to images acquired during the migraine-free state. When normalized ASL images acquired 30 min after treatment were compared with those acquired during the attack, relative improvement of perfusion in the bilateral median thalamic areas including hypothalamus was observed. Hypothalamus and its surrounding areas may participate in the pathogenesis in migraine attack.

A novel rodent model of reperfusion injury following occlusion of the middle cerebral artery

We have developed a novel rodent animal model of reperfusion injury following stroke. In this model, blood flow through the middle cerebral artery (MCA) is temporarily occluded by placing gentle pressure on sutures behind the artery along three separate branches. The sutures remain in place for a period of time (occlusion), and are then removed for an additional amount of time (reperfusion) to study the effects of drug treatment on the ischemic core and/or reperfusion injury. This approach resulted in a highly reproducible focal infarct restricted to the prefrontal cerebral cortex with an intra-operative mortality rate of less than 1%. To validate this new model of reperfusion injury, we used two well characterized neuroprotectants, estrogen and edaravone. Estrogen and edaravone have been studied extensively in many animal models, and our lab as well as others have consistently demonstrated significant reductions in infarct size following edaravone or estrogen pretreatment. In this novel model, intravenous pretreatment of animals with either estrogen or edaravone resulted in significant, dose-dependent, reduction in infarct size following reperfusion. In conclusion, our results demonstrate the validity of using this novel model to study the mechanism of neuroprotection following stroke. Based on the low mortality rate and reproducibility of the focal infarct volume, this novel rodent model is ideal for preclinical studies to screen drugs for potential therapy against reperfusion injury following stroke.

Mapping resting-state brain networks in conscious animals

In the present study we mapped brain functional connectivity in the conscious rat at the "resting state" based on intrinsic blood-oxygenation-level dependent (BOLD) fluctuations. The conscious condition eliminated potential confounding effects of anesthetic agents on the connectivity between brain regions. Indeed, using correlational analysis we identified multiple cortical and subcortical regions that demonstrated temporally synchronous variation with anatomically well-defined regions that are crucial to cognitive and emotional information processing including the prefrontal cortex (PFC), thalamus and retrosplenial cortex. The functional connectivity maps created were stringently validated by controlling for false positive detection of correlation, the physiologic basis of the signal source, as well as quantitatively evaluating the reproducibility of maps. Taken together, the present study has demonstrated the feasibility of assessing functional connectivity in conscious animals using fMRI and thus provided a convenient and non-invasive tool to systematically investigate the connectional architecture of selected brain networks in multiple animal models.

Prolonged gum chewing evokes activation of the ventral part of prefrontal cortex and suppression of nociceptive responses: involvement of the serotonergic system

We have proposed a concept that prolonged rhythmic gum chewing causes a suppressed nociceptive flexion reflex via the serotonergic (5-HT) descending inhibitory pathway. However, the mechanism of activation of the 5-HT system by gum chewing remains undetermined. Several human and animal studies have reported that a direct connection exists between the prefrontal cortex (PFC) and 5-HT neurons in the dorsal raphe nucleus; therefore, we hypothesized that activation of the PFC region might be responsible for augmented 5-HT activity. To evaluate this hypothesis, oxygenated hemoglobin (oxyHb) and deoxygenated hemoglobin concentrations in the PFC were measured in the PFC during a 20-min time period of gum chewing using 24-channel near-infrared spectroscopy. A significant increase in oxyHb level was observed in the ventral part of PFC compared with the dorsal part of PFC. We confirmed the previous results in that the nociceptive flexion reflex was significantly suppressed and the 5-HT level in blood was significantly increased following prolonged gum chewing. These results support the hypothesis that activation of the ventral part of PFC during gum chewing evokes augmented activity of 5-HT neurons in the dorsal raphe nucleus, which in turn suppress nociceptive responses.

Neural mechanisms associated with food motivation in obese and healthy weight adults

One out of three adults in the United States is clinically obese. Excess food intake is associated with food motivation, which has been found to be higher in obese compared to healthy weight (HW) individuals. Little is known, however, regarding the neural mechanisms associated with food motivation in obese compared to HW adults. The current study used functional magnetic resonance imaging (fMRI) to examine changes in the hemodynamic response in obese and HW adults while they viewed food and nonfood images in premeal and postmeal states. During the premeal condition, obese participants showed increased activation, compared to HW participants, in anterior cingulate cortex (ACC) and medial prefrontal cortex (MPFC). Moreover, in the obese group, self-report measures of disinhibition were negatively correlated with premeal ACC activations and self-report measures of hunger were positively correlated with premeal MPFC activations. During the postmeal condition, obese participants also showed greater activation than HW participants in the MPFC. These results indicate that brain function associated with food motivation differs in obese and HW adults and may have implications for understanding brain mechanisms contributing to overeating and obesity, and variability in response to diet interventions.