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Mauricio R Delgado

Publications and source records attributed to Mauricio R Delgado.

At least 19 recordsLinked to original sources
PubMed2006

How personal experience modulates the neural circuitry of memories of September 11.

Brown and Kulik [Brown R, Kulik J (1977) Cognition 5:73-99] introduced the term "flashbulb memory" to describe the recall of shocking, consequential events such as hearing news of a presidential assassination. They proposed that the vivid detail of such memories results from the action of a unique neural mechanism. In the present study of personal recollections of the terrorist attacks of September 11, 2001 (9/11) in New York City, we combine behavioral and brain imaging techniques, with two goals: (i) to explore the neural basis of such memories and (ii) to clarify the characteristics of the emotional events that may give rise to them. Three years after the terrorist attacks, participants were asked to retrieve memories of 9/11, as well as memories of personally selected control events from 2001. At the time of the attacks, some participants were in Downtown Manhattan, close to the World Trade Center; others were in Midtown, a few miles away. The Downtown participants exhibited selective activation of the amygdala as they recalled events from 9/11, but not while they recalled control events. This was not the case for the Midtown participants. Moreover, only the Downtown participants reported emotionally enhanced recollective experiences while recalling events from 9/11, as compared with control events. These results suggest that close personal experience may be critical in engaging the neural mechanisms that underlie the emotional modulation of memory and thus in producing the vivid recollections to which the term flashbulb memory is often applied.

Adult↗
PubMed2006

Factor analysis of neuroanatomical and clinical characteristics of holoprosencephaly.

The objective of this study is to better understand the relationship between neuroradiologic and clinical characteristics in holoprosencephaly (HPE) using the multivariate analysis called factor analysis. HPE is a brain malformation characterized by incomplete cleavage of the cerebral hemispheres and deep gray structures. We performed evaluations on 89 children with HPE that included their history, developmental assessment, and physical examination. Ten clinical variables included in factor analysis were the grade of spasticity, dystonia, choreoathetosis, hypotonia, mobility, upper extremity/hand function, expressive language, feeding/swallowing difficulty, endocrinopathies, and temperature dysregulation. Five neuroimaging variables graded by pediatric neuroradiologists were the grade of HPE (from least to most severe: lobar, semilobar, and alobar) and the degree of non-separation of caudate, lentiform, thalamic, and hypothalamic nuclei. Factor analysis using principle component extraction and varimax rotation was utilized. Four significant factors were identified: (1) neuroimaging/developmental factor, (2) motor factor, (3) hypothalamic/oromotor factor, and (4) hypotonia factor. These four factors accounted for 65.2% of the variance. In this factor analysis of HPE patients, we were able to reduce the large number of clinical and radiological variables into four factors. These factors and the constructs underlying them provide structure to the data and provide key parameters for future studies involving neurodevelopmental outcomes in HPE.

Brain↗
PubMed2006

Performance feedback drives caudate activation in a phonological learning task.

Adults have difficulty discriminating nonnative phonetic contrasts, but under certain circumstances training can lead to improvement in this ability. Despite the ubiquitous use of performance feedback in training paradigms in this and many other domains, the mechanisms by which feedback affects learning are not well understood. In this event-related functional magnetic resonance imaging study, we examined how performance feedback is processed during perceptual learning. Thirteen Japanese speakers for whom the English phonemes [r] and [l] were nondistinct performed an identification task of the words "road" and "load" that has been shown to be effective in inducing learning only when performance feedback is present. Each subject performed alternating runs of training with and without feedback, followed by performance of a card-guessing task with monetary reward and punishment outcomes. We found that the caudate nucleus was more robustly activated bilaterally when performing the perceptual identification task with feedback than without feedback, and the right caudate nucleus also showed a differential response to positive and negative feedback. Moreover, using a within-subjects design, we found that the caudate nucleus also showed a similar activation pattern to monetary reward and punishment outcomes in the card-guessing task. These results demonstrate that the caudate responds to positive and negative feedback during learning in a manner analogous to its processing of extrinsic affective reinforcers and indicate that this region may be a critical moderator of the influence of feedback on learning. These findings impact our broader understanding of the mechanisms underlying nondeclarative learning and language acquisition.

Adult↗
PubMed2006

Definition and classification of negative motor signs in childhood.

In this report we describe the outcome of a consensus meeting that occurred at the National Institutes of Health in Bethesda, Maryland, March 12 through 14, 2005. The meeting brought together 39 specialists from multiple clinical and research disciplines including developmental pediatrics, neurology, neurosurgery, orthopedic surgery, physical therapy, occupational therapy, physical medicine and rehabilitation, neurophysiology, muscle physiology, motor control, and biomechanics. The purpose of the meeting was to establish terminology and definitions for 4 aspects of motor disorders that occur in children: weakness, reduced selective motor control, ataxia, and deficits of praxis. The purpose of the definitions is to assist communication between clinicians, select homogeneous groups of children for clinical research trials, facilitate the development of rating scales to assess improvement or deterioration with time, and eventually to better match individual children with specific therapies. "Weakness" is defined as the inability to generate normal voluntary force in a muscle or normal voluntary torque about a joint. "Reduced selective motor control" is defined as the impaired ability to isolate the activation of muscles in a selected pattern in response to demands of a voluntary posture or movement. "Ataxia" is defined as an inability to generate a normal or expected voluntary movement trajectory that cannot be attributed to weakness or involuntary muscle activity about the affected joints. "Apraxia" is defined as an impairment in the ability to accomplish previously learned and performed complex motor actions that is not explained by ataxia, reduced selective motor control, weakness, or involuntary motor activity. "Developmental dyspraxia" is defined as a failure to have ever acquired the ability to perform age-appropriate complex motor actions that is not explained by the presence of inadequate demonstration or practice, ataxia, reduced selective motor control, weakness, or involuntary motor activity.

Apraxias↗
PubMed2005

Instructed smoking expectancy modulates cue-elicited neural activity: a preliminary study.

In recent years, research applying functional neuroimaging to the study of cue-elicited drug craving has emerged. This research has begun to identify a distributed system of brain activity during drug craving. A review of this literature suggested that expectations regarding the opportunity to use a drug affected the pattern of neural responses elicited by drug cues. Using functional magnetic resonance imaging (fMRI), we examined the effects of smoking expectancy on the neural response to neutral (e.g., roll of tape) and smoking-related (a cigarette) stimuli in male cigarette smokers deprived of nicotine for 8 hr. As predicted, several brain regions (e.g., the anterior cingulate cortex) exhibited differential activation during cigarette versus neutral cue exposure. Moreover, we found that subregions of the prefrontal cortex (i.e., ventromedial, ventrolateral, and dorsolateral prefrontal cortices) showed cue-elicited activation that was modulated by smoking expectancy. These results highlight the importance of perceived drug use opportunity in the neurobiological response to drug cues.

Adult↗
PubMed2005

Endocrine disorders associated with holoprosencephaly.

OBJECTIVE: To investigate the incidence of endocrinopathies in holoprosencephaly (HPE) and correlate the severity of the endocrinopathies with the neuroanatomic abnormalities. STUDY DESIGN: We reviewed the histories and medical records of 117 children with HPE for endocrinopathies and related treatments. Neuroimaging studies were graded for severity of HPE, hypothalamus non-separation, and pituitary abnormalities. RESULTS: Diabetes insipidus (DI) occurred in 70% of patients with classic HPE. The severity of the DI correlated with the grade of HPE and hypothalamic non-separation (p < 0.0001). Anterior pituitary dysfunctions were much less common. Hypothyroidism was identified in 11% of patients, hypocorticism in 7%, and growth hormone deficiency in 5%. Only one patient with middle interhemispheric variant of holoprosencephaly (MIH) had any of these disorders. CONCLUSIONS: Patients with HPE have a high incidence of DI that may be related to the failure of cleavage of hypothalamic nuclei. Anterior pituitary dysfunctions are much less common than DI.

Adolescent↗
PubMed2004

How emotion enhances the feeling of remembering.

Studies examining memories of arousing 'real-life' events show that emotion heightens the feeling of remembering, without necessarily enhancing the objective accuracy of the memories. We measured brain activity associated with the feeling of remembering emotional and neutral photos. Subjects indicated whether recognition was accompanied by a recollection of details about the study episode ('remember') or not ('know'). 'Remember' judgments were boosted for emotional photos, but accuracy did not differ. For neutral photos, 'remember' judgments were related to enhanced activity in the parahippocampal cortex, previously related to recognition of visual details, which one might expect to supply the retrieval clues for a 'remember' judgment. In contrast, 'remember' judgments for emotional photos were associated with enhanced activity in the amygdala, suggesting that subjects rely on arousal and perceptual fluency to evaluate these memories. For the first time, we identify the neural mechanisms underlying the enhanced feeling of remembering for emotional events.

Adult↗
PubMed2004

Extinction learning in humans: role of the amygdala and vmPFC.

Understanding how fears are acquired is an important step in translating basic research to the treatment of fear-related disorders. However, understanding how learned fears are diminished may be even more valuable. We explored the neural mechanisms of fear extinction in humans. Studies of extinction in nonhuman animals have focused on two interconnected brain regions: the amygdala and the ventral medial prefrontal cortex (vmPFC). Consistent with animal models suggesting that the amygdala is important for both the acquisition and extinction of conditioned fear, amygdala activation was correlated across subjects with the conditioned response in both acquisition and early extinction. Activation in the vmPFC (subgenual anterior cingulate) was primarily linked to the expression of fear learning during a delayed test of extinction, as might have been expected from studies demonstrating this region is critical for the retention of extinction. These results provide evidence that the mechanisms of extinction learning may be preserved across species.

Adolescent↗
PubMed2004

A retrospective survey of perinatal risk factors of 104 living children with holoprosencephaly.

Holoprosencephaly (HPE) is a brain malformation resulting from a primary defect in development of the basal forebrain during early gestation. Prenatal genetic and environmental factors and birth outcomes were described in a population of 104 children with holoprosencephaly referred to three clinical centers from 1998 through 2002. The mean child age was 4 years. Of cases karyotyped, 9% presented with a chromosomal abnormality. This study of living children with holoprosencephaly, the majority of whom are cytogenetically normal, provides new information on the subsample of children with a less severe phenotype. Most children were born at term; about 51% were microcephalic at birth. Consistent with previous research, the association between HPE and maternal history of diabetes merits further investigation. Several findings have important implications for future research. Only 22% of the children in this study sample were diagnosed with holoprosencephaly prenatally. The vast majority of children (72%) were diagnosed with HPE between birth and 1 year of age. Also, 19% of the cases referred to the Carter Centers with HPE were not confirmed on scan review. When possible, future population-based epidemiological studies should emphasize mechanisms that identify children with HPE outside of the newborn period and confirm the diagnosis by review of MRI or high quality CT brain scan.

Adolescent↗
PubMed2004

Event-related functional magnetic resonance imaging of reward-related brain circuitry in children and adolescents.

BACKGROUND: Functional disturbances in reward-related brain systems are thought to play a role in the development of mood, impulse, and substance-abuse disorders. Studies in nonhuman primates have identified brain regions, including the dorsal/ventral striatum and orbital-frontal cortex, in which neural activity is modulated by reward. Recent studies in adults have concurred with these findings by observing reward-contingent blood oxygen level-dependent (BOLD) responses in these regions during functional magnetic resonance imaging (fMRI) paradigms; however, no previous studies indicate whether comparable modulations of neural activity exist in the brain reward systems of children and adolescents. METHODS: We used event-related fMRI and a behavioral paradigm modeled on previous work in adults to study brain responses to monetary gains and losses in psychiatrically healthy children and adolescents as part of a program examining the neural substrates of anxiety and depression in youth. RESULTS: Regions and time-courses of reward-related activity were similar to those observed in adults with condition-dependent BOLD changes in the ventral striatum and lateral and medial orbital-frontal cortex; specifically, these regions showed larger responses to positive than to negative feedback. CONCLUSIONS: These results provide further evidence for the value of event-related fMRI in examining reward systems of the brain, demonstrate the feasibility of this approach in children and adolescents, and establish a baseline from which to understand the pathophysiology of reward-related psychiatric disorders in youth.

Adolescent↗
PubMed2004

Modulation of caudate activity by action contingency.

Research has increasingly implicated the striatum in the processing of reward-related information in both animals and humans. However, it is unclear whether human striatal activation is driven solely by the hedonic properties of rewards or whether such activation is reliant on other factors, such as anticipation of upcoming reward or performance of an action to earn a reward. We used event-related functional magnetic resonance imaging to investigate hemodynamic responses to monetary rewards and punishments in three experiments that made use of an oddball paradigm. We presented reward and punishment displays randomly in time, following an anticipatory cue, or following a button press response. Robust and differential activation of the caudate nucleus occurred only when a perception of contingency existed between the button press response and the outcome. This finding suggests that the caudate is involved in reinforcement of action potentially leading to reward, rather than in processing reward per se.

Adult↗
PubMed2004

Functional dissociations within the inferior parietal cortex in verbal working memory.

Neuroimaging studies of working memory have revealed two sites in the left supramarginal gyrus that may support the short-term storage of phonological information. Activation in the left dorsal aspect of the inferior parietal cortex (DIPC) has been observed in contrasts of working memory load, whereas activation in the ventral aspect of the inferior parietal cortex (VIPC) has been found primarily in contrast of information type (verbal vs. nonverbal). Our goal was to determine whether these two areas are functionally distinct or if instead they are part of a homogeneous region with large variations in the focus of peak activity. Toward this end, we used fMRI to assess the neural response in two working memory tasks (N-back and item recognition) in which we also manipulated memory load and the type of information to be recalled (verbal vs. nonverbal). We found both DIPC and VIPC activation in the same group of subjects and further demonstrated that they have differential sensitivity to our experimental factors. Only the DIPC showed robust load effects, whereas only the VIPC showed reliable effects of information type. These results help to account for the differences observed in between-subject comparisons, and they indicate that the two regions are functionally dissociable. In contrast to the DIPC, activity of the VIPC was also recruited in the fixation and low-load conditions, a surprising result that has not been fully explored in prior studies. Despite their distinctive patterns of performance, neither of these regions displayed a pattern of activity that entirely corresponds to common assumptions of a dedicated phonological short-term store (STS). Instead, we hypothesize that the DIPC may support domain-general executive processes, while the VIPC may support phonological encoding-recoding processes central to a variety of language tasks.

Adult↗
PubMed2003

Seizure remission and antiepileptic drug discontinuation in children with tuberous sclerosis complex.

BACKGROUND: Epilepsy is a common neurologic complication of tuberous sclerosis complex (TSC) and it is often refractory to treatment. Therefore, treating physicians are often reluctant to discontinue antiepileptic drugs (AEDs) in individuals with TSC who have attained seizure remission. To our knowledge, seizure remission and AED discontinuation in children with TSC has not been studied. OBJECTIVE: To characterize seizure remission and AED discontinuation in children with TSC. METHODS: Retrospective medical record and neuroimaging analysis of 15 children with TSC and epilepsy who had seizure remission, with a subsequent trial of discontinuation of AED treatment. RESULTS: The seizure remission rate for the group of patients with TSC and epilepsy was 14.2%. From the group of 15 patients who had a remission, the absolute relapse rate was 26.7% after a mean follow-up of 5 years 7 months. Patients with sustained remission were more likely to have normal intelligence and only a few cortical or subcortical lesions on neuroimaging. CONCLUSIONS: The proportion of children with TSC and epilepsy who achieve seizure remission is small. Nevertheless, some do attain seizure remission, and AEDs may be successfully discontinued. Mild cerebral involvement is a general clinical marker for seizure remission. The relapse rate in those who have undergone a trial of discontinuation of AED therapy is comparable with the rate in the general pediatric population with epilepsy.

Adolescent↗
PubMed2003

Electroencephalography in holoprosencephaly: findings in children without epilepsy.

OBJECTIVE: To evaluate the electroencephalographic characteristics of patients with holoprosencephaly (HPE) without epilepsy. METHODS: We evaluated the electroencephalograms (EEGs) of 18 children with HPE who lacked a history of seizures. Neuroimaging studies were assessed for severity of HPE and thalamic non-separation and the presence of dorsal cysts and cortical malformations. RESULTS: Hypersynchronous theta activity occurred in 50 and 60% of EEGs during wakefulness or drowsiness/sleep, respectively, and correlated with the grade of thalamic non-separation (p<0.05). Hypersynchronous beta activity during sleep occurred in 41% of EEGs. Posterior amplitude attenuation occurred in 33% of EEGs and correlated with the presence of a dorsal cyst (p</=0.0004). Photic driving responses were seen in 50% of the EEGs. If a dorsal cyst was present, the responses were anteriorly displaced. Epileptiform activity was noted in EEGs of 5 patients and did not correlate with the incidence of clinical seizures. CONCLUSIONS: Hypersynchronous activity was present frequently in EEGs of HPE patients, possibly attributable to incomplete separation of the thalami and hemispheres. Dorsal cysts were associated with posterior amplitude attenuation and anterior displacement of the photic response. In this selective cohort, the presence of epileptiform activity was not a risk factor for seizures. SIGNIFICANCE: To date, this is the largest study of EEGs in children diagnosed with HPE without seizures. This study complements our earlier clinical and neuroradiologic studies by providing neurophysiologic data that serves to enhance our understanding of this complex, rare disorder.

Adolescent↗
PubMed2003

Movement disorders in children: definitions, classifications, and grading systems.

Disorders that affect movement in children are relatively common. However, they have received little attention, especially when compared with epilepsy and neuromuscular disorders. In this review article, we address the major types of movement disorders that affect children, their clinical characteristics and etiologies, and, when available, the scales used to grade them. A discussion on spasticity, which traditionally is not addressed in reviews of "movement disorders," is also included.

Ataxia↗
PubMed2003

Classification and definition of disorders causing hypertonia in childhood.

OBJECTIVE: This report describes the consensus outcome of an interdisciplinary workshop that was held at the National Institutes of Health in April 2001. The purpose of the workshop and this article are to define the terms "spasticity," "dystonia," and "rigidity" as they are used to describe clinical features of hypertonia in children. The definitions presented here are designed to allow differentiation of clinical features even when more than 1 is present simultaneously. METHODS: A consensus agreement was obtained on the best current definitions and their application in clinical situations. RESULTS: "Spasticity" is defined as hypertonia in which 1 or both of the following signs are present: 1) resistance to externally imposed movement increases with increasing speed of stretch and varies with the direction of joint movement, and/or 2) resistance to externally imposed movement rises rapidly above a threshold speed or joint angle. "Dystonia" is defined as a movement disorder in which involuntary sustained or intermittent muscle contractions cause twisting and repetitive movements, abnormal postures, or both. "Rigidity" is defined as hypertonia in which all of the following are true: 1) the resistance to externally imposed joint movement is present at very low speeds of movement, does not depend on imposed speed, and does not exhibit a speed or angle threshold; 2) simultaneous co-contraction of agonists and antagonists may occur, and this is reflected in an immediate resistance to a reversal of the direction of movement about a joint; 3) the limb does not tend to return toward a particular fixed posture or extreme joint angle; and 4) voluntary activity in distant muscle groups does not lead to involuntary movements about the rigid joints, although rigidity may worsen. CONCLUSION: We have provided a set of definitions for the purpose of identifying different components of childhood hypertonia. We encourage the development of clinical rating scales that are based on these definitions, and we encourage research to relate the degree of hypertonia to the degree of functional ability, change over time, and societal participation in children with motor disorders.

Child↗
PubMed2003

Middle interhemispheric variant of holoprosencephaly associated with diffuse polymicrogyria.

An 11-month-old boy was discovered to have a cleft palate, club foot, hypospadias, and myoclonic seizures. No in utero exposure to teratogens was identified. Brain MR imaging revealed a middle interhemispheric fusion variant of holoprosencephaly, diffuse polymicrogyria, and a hypoplastic brain stem; this was a distinctly unusual association of findings. We hypothesize that an unknown genetic factor causes disturbances of cleavage of the prosencephalon as well as neuronal migration and organization.

Abnormalities, Multiple↗