PubMed · 6569456
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M H Rajabally. 1984. Research problems: objectivity.. https://pubmed.ncbi.nlm.nih.gov/6569456/
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This article focuses on gradient-based backpropagation algorithms that use either a common adaptive learning rate for all weights or an individual adaptive learning rate for each weight and apply the Goldstein/Armijo line search. The learning-rate adaptation is based on descent techniques and estimates of the local Lipschitz constant that are obtained without additional error function and gradient evaluations. The proposed algorithms improve the backpropagation training in terms of both convergence rate and convergence characteristics, such as stable learning and robustness to oscillations. Simulations are conducted to compare and evaluate the convergence behavior of these gradient-based training algorithms with several popular training methods.
CONTEXT: Disasters expose unselected populations to traumatic events and can be used to study the mental health effects. The Oklahoma City, Okla, bombing is particularly significant for the study of mental health sequelae of trauma because its extreme magnitude and scope have been predicted to render profound psychiatric effects on survivors. OBJECTIVE: To measure the psychiatric impact of the bombing of the Alfred P. Murrah Federal Building in Oklahoma City on survivors of the direct blast, specifically examining rates of posttraumatic stress disorder (PTSD), diagnostic comorbidity, functional impairment, and predictors of postdisaster psychopathology. DESIGN, SETTING, AND PARTICIPANTS: Of 255 eligible adult survivors selected from a confidential registry, 182 (71%) were assessed systematically by interviews approximately 6 months after the disaster, between August and December 1995. MAIN OUTCOME MEASURES: Diagnosis of 8 psychiatric disorders, demographic data, level of functioning, treatment, exposure to the event, involvement of family and friends, and physical injuries, as ascertained by the Diagnostic Interview Schedule/Disaster Supplement. RESULTS: Forty-five percent of the subjects had a postdisaster psychiatric disorder and 34.3% had PTSD. Predictors included disaster exposure, female sex (for any postdisaster diagnosis, 55% vs 34% for men; chi2 = 8.27; P=.004), and predisaster psychiatric disorder (for PTSD, 45% vs 26% for those without predisaster disorder; chi2 = 6.86; P=.009). Onset of PTSD was swift, with 76% reporting same-day onset. The relatively uncommon avoidance and numbing symptoms virtually dictated the diagnosis of PTSD (94% meeting avoidance and numbing criteria had full PTSD diagnosis) and were further associated with psychiatric comorbidity, functional impairment, and treatment received. Intrusive reexperience and hyperarousal symptoms were nearly universal, but by themselves were generally unassociated with other psychopathology or impairment in functioning. CONCLUSIONS: Our data suggest that a focus on avoidance and numbing symptoms could have provided an effective screening procedure for PTSD and could have identified most psychiatric cases early in the acute postdisaster period. Psychiatric comorbidity further identified those with functional disability and treatment need. The nearly universal yet distressing intrusive reexperience and hyperarousal symptoms in the majority of nonpsychiatrically ill persons may be addressed by nonmedical interventions of reassurance and support.
Behavioral and physiological effects of partial kindling of the right ventral hippocampus by perforant path (PP) stimulation were investigated in the cat. Partial kindling produced lasting changes in affect (increased defensive response to rats) and predatory attack (decreased pawing and biting attack). Partial kindling also induced long term potentiation (LTP) of amygdala efferent transmission to ventromedial hypothalamus (VMH) and periaqueductal gray (PAG) in left and right hemispheres. LTP of field population spikes evoked in area CA3 by PP stimulation was also observed. LTP was detected using evoked potential methods. These findings parallel previous studies of left PP-CA3 partial kindling. Analysis of covariance removing effects of LTP from behavioral changes suggests that initiation of increased defensiveness at 2 days after completion of partial kindling depended on LTP of left and right amygdalo-VMH and right amygdalo-PAG transmission. From 6 days after kindling onward, increased defensiveness depended on LTP of right amygdalo-PAG transmission. Depotentiation of amygdala efferent LTP by bilateral low frequency amygdala stimulation (LFS) (900 pulses at 1 Hz, once daily for 7 days) selectively reduced LTP in right amygdala efferents. At the same time, defensive, but not predatory attack behavior, was returned to levels seen prior to partial kindling. Both depotentiation and reduction of defensiveness were transient. Defensiveness increased to post-kindling levels by 76 days after LFS. At the same time, LTP was restored in the right amygdalo-PAG pathway. In contrast LTP in the right amygdalo-VMH pathway remained depotentiated. Effects of LFS were not due to damage, as thresholds to evoke amygdala efferent response were unchanged. These findings suggest that lasting change in affect following partial hippocampal kindling depends on LTP of right amygdala efferent transmission to PAG. The findings parallel studies of non-convulsant pharmacological induction of lasting increases in defensiveness and amygdalo-PAG LTP with FG-7142. The parallel between the present findings and the FG-7142 experiments suggests that lasting changes in defensive response are dependent on LTP of right amygdala efferents to the PAG, however produced. The findings suggest further that the spectrum of behavioral changes produced by partial kindling are dependent on changes in a variety of neural circuits, and that amygdala efferent transmission changes are responsible for changes in defensive behavior, but not predatory attack behavior. Clinical implications are discussed.