Brain mechanisms in fatal cardiac arrhythmia

Intravenous injection of histamine to rabbits was used as a prototype in an investigation of the mechanism of sudden death due to anaphylaxis and other causes. The “dive” reflex, bradycardia due to activation of the ophthalmic branch of the fifth cranial nerve, was induced in thirty-seven of the animals while they inhaled a very small amount of cigarette smoke. Associated with the resulting bradycadia were lowered blood pH and increased serum content of lactic acid and potassium and increased peripheral arterial constriction with elevation of diastolic blood pressure. Intravenous injection of 1 ml of histamine in the presence of the dive reflex induced potentially fatal ventricular arrhythmia, but no cardiac disturbance when administered while the dive reflex was inactive, thereby strongly suggesting that sudden death in anaphylaxis may involve an overzealous response to a normally protective neural reflex.     

Brain mechanisms of altered consciousness in generalised seizures

In spite of the inherent difficulties in achieving a biologically meaningful definition of consciousness, recent neurophysiological studies are starting to provide some insight in fundamental mechanisms associated with impaired consciousness in neurological disorders. Generalised seizures are associated with disruption of the default state network, a functional network of discrete brain areas, which include the fronto-parietal cortices. Subcortical contribution through activation of thalamocortical structures, as well as striate nuclei are also crucial to produce impaired consciousness in generalised seizures.     

Brain mechanisms of altered consciousness in focal seizures

Consciousness is a central concept in epileptology, relevant to the understanding of both focal and generalized seizures. Within focal seizures, impairment of consciousness has long been considered as the main criterion differentiating complex partial seizures (CPS) from simple partial seizures With the development of improved tools for investigating human brain function, new insights into the brain mechanisms of altered consciousness in CPS have become available. This paper reviews the existing literature on how the currently available methods can be used to address the fundamental issue of how CPS alter consciousness.     

Brain mechanisms and intelligence. Psychometric g and executive function

Sternberg [Sternberg, R.J. (1985). Beyond IQ: a triarchic theory of human intelligence. New York: Cambridge Univ. Press.] has proposed that the general intelligence, or the g factor, obtained when batteries of mental tests are factor analyzed, is a reflection of the fact that executive functions (EF) are common to all cognitive tests. Three lines of evidence that fail to support Sternberg's formulation are presented. First, in animal problem solving studies, there is only a modest degree of overlap between brain structures that are critical for g, and brain structures that have been identified as the rodent EF system. Second, children with attention deficit-hyperactivity disorder (ADHD), characterized by EF dysfunction, do not have IQ scores that are lower, on average, than children in the test standardization populations. Third, human frontal lobe patients often have clear EF deficits, but IQ (a next-best estimate of g) may be preserved. These findings cast serious doubt on the plausibility of Sternberg's formulation. Clarifying the distinction between psychometric g and EF can be important for understanding the differences between practical and psychometric intelligence.     

Brain mechanisms of extinction of the classically conditioned eyeblink response

It is well established that the cerebellum and its associated circuitry are essential for classical conditioning of the eyeblink response and other discrete motor responses (e.g., limb flexion, head turn, etc.) learned with an aversive unconditioned stimulus (US). However, brain mechanisms underlying extinction of these responses are still relatively unclear. Behavioral studies have demonstrated extinction as an active learning process distinct from acquisition. Experimental data in eyeblink conditioning suggest that plastic changes specific to extinction may play an important role in this process. Both cerebellar and hippocampal systems may be involved in extinction of these memories. The nature of this phenomenon and identification of the neural substrates necessary for extinction of originally learned responses is the topic of this review.     

Respiratory sinus arrhythmia during stress predicts resting respiratory sinus arrhythmia 3 years later in a pediatric sample.

The author examined whether respiratory sinus arrhythmia (RSA) responses to stress predicted resting RSA approximately 3 years later in children and adolescents. A total of 149 children and adolescents (49% girls and women, 44% African Americans) participated in 2 laboratory protocols approximately 3 years apart. RSA reactivity during tasks was consistent within participants across tasks during each session. Resting RSA at Visit 1 explained 17% of the variance in resting RSA at Visit 2 when body mass index, duration between visits, race, gender, and age were controlled for. Visit 1 RSA reactivity explained an additional 5% of the variance in resting RSA at Visit 2. The positive relationship between Visit 1 reactivity and Visit 2 resting levels suggests that larger decreases in RSA during stress predicted lower resting RSA. Conversely, increases in RSA during stress were associated with higher resting RSA an average of 3 years later.     

Subcortical mechanisms in language: lexical-semantic mechanisms and the thalamus.

Four previously published cases of dominant thalamic lesion in which the author has participated are reviewed to gain a better understanding of thalamic participation in lexical-semantic functions. Naming deficits in two cases support Nadeau and Crosson's (1997) hypothesis of a selective engagement mechanism involving the frontal lobes, inferior thalamic peduncle, nucleus reticularis, and other thalamic nuclei, possibly the centromedian nucleus. This mechanism selectively engages those cortical areas required to perform a cognitive task, while maintaining other areas in a state of relative disengagement. Deficits in selective engagement disproportionately affect lexical retrieval based on semantic input, as opposed to lexical and sublexical processes, because the former is more dependent upon this attentional system. The concept of selective engagement is also useful in understanding thalamic participation in working memory, as supported by data from one recent functional neuroimaging study. Other processes also may be compromised in more posterior thalamic lesions which damage the pulvinar but not other components of this selective engagement system. A third case with aphasia after a more superior and posterior thalamic lesion also had oral reading errors similar to those in neglect dyslexia. The pattern of deficits suggested a visual processing problem in the early stages of reading. The fourth case had a category-specific naming deficit after posterior thalamic lesion. Taken together, the latter two cases indicate that the nature of language functions in more posterior regions of the dominant thalamus depends upon the cortical connectivity of the thalamic region. Together, findings from the four cases suggest that thalamic nuclei and systems are involved in multiple processes which directly or indirectly support cortical language functions.     

Brain mechanisms involved in angry prosody change detection in school-age children and adults,revealed by electrophysiology

Voices transmit social signals through speech and/or prosody. Emotional prosody conveys key information about the emotional state of a speaker and is thus a crucial cue that one has to detect in order to develop efficient social communication. Previous studies in adults reported different brain responses to emotional than to neutral prosodic deviancy. The aim of this study was to characterize such specific emotional deviancy effects in school-age children. The mismatch negativity (MMN) and P3a evoked potentials, reflecting automatic change detection and automatic attention orienting, respectively, were obtained for neutral and emotional angry deviants in both school-age children (n = 26) and adults (n = 14). Shorter latencies were found for emotional than for neutral preattentional responses in both groups. However, whereas this effect was observed on the MMN in adults, it appeared in an early discriminative negativity preceding the MMN in children. A smaller P3a amplitude was observed for the emotional than for the neutral deviants at all ages. Overall, the brain responses involved in specific emotional change processing are already present during childhood, but responses have not yet reached an adult pattern. We suggest that these processing differences might contribute to the known improvement of emotional prosody perception between childhood and adulthood.     

Brain mechanisms associated with background monitoring of the environment for potentially significant sensory events

Background monitoring is a necessary prerequisite to detect unexpected changes in the environment, while being involved in a primary task. Here, we used fMRI to investigate the neural mechanisms that underlie adaptive goal-directed behavior in a cued task switching paradigm during real response conflict or, more generally, when expectations on the repetitive features of the environment were violated. Unexpected changes in sensory stimulus attributes in the currently unattended stimulus dimension thereby led to activations in a bilateral network comprising inferior lateral frontal, intraparietal, and posterior medial frontal brain regions, independent of whether these attributes elicited a factual response conflict or not. This fronto-parietal network may thus play an important role in adaptive responding to potentially significant events outside the current focus of attention.     

Ferenczi's fatal illness in historical context

In August 1932, Ferenczi was already manifesting symptoms of his fatal illness, pernicious anemia. This was diagnosed between September 20 and October 2 of that year, less than a month after the Twelfth International Psychoanalytic Congress in Wiesbaden. Despite seemingly successful treatment with injectable liver extract, he underwent an acute psychotic episode in March 1933, triggered by the neurological symptoms of his illness. These facts substantiate the subsequent claim of Freud and Jones that Ferenczi suffered from paranoia near the end of his life, but they do not support the commonly-held view that the writings and experiments in psychoanalytic technique of his last five years were symptomatic of a progressive mental illness.     

Learning mechanisms in matching to sample.

A model system and an experiment on early learning and decision processes in matching-to-sample and oddity-from-sample tasks are presented. The model system is based, in part, on videotaped records of pigeons' looking responses before they chose 1 of 2 comparison stimuli. In order to see the wavelength stimuli recessed behind the pecking keys, the pigeons had to move in front of them. Although there were slight increases in the acceptance probability with switches between the stimuli before a choice response, the overall decision strategy was close to a Markov choice process in which choice proportions could be predicted by the product of each rejection probability and the final acceptance probability. Learning involved learning to discriminate rather than learning to adopt a stricter criterion for an acceptable sample match.     

Brain mechanisms for predictive control by switching internal models: implications for higher-order cognitive functions

Humans can guide their actions toward the realization of their intentions. Flexible, rapid and precise realization of intentions and goals relies on the brain learning to control its actions on external objects and to predict the consequences of this control. Neural mechanisms that mimic the input–output properties of our own body and other objects can be used to support prediction and control, and such mechanisms are called internal models. We first summarize functional neuroimaging, behavioral and computational studies of the brain mechanisms related to acquisition, modular organization, and the predictive switching of internal models mainly for tool use. These mechanisms support predictive control and flexible switching of intentional actions. We then review recent studies demonstrating that internal models are crucial for the execution of not only immediate actions but also higher-order cognitive functions, including optimization of behaviors toward long-term goals, social interactions based on prediction of others’ actions and mental states, and language processing. These studies suggest that a concept of internal models can consistently explain the neural mechanisms and computational principles needed for fundamental sensorimotor functions as well as higher-order cognitive functions. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Increased cardiac awareness in panic disorder.

We investigated cardiac perception in panic disorder with both self-report and objective measures. In Study 1, 120 patients with panic disorder, 86 infrequent panickers, and 38 patients with other anxiety disorders reported greater cardiac and gastrointestinal awareness than 62 normal control subjects. Subjects with panic attacks reported greater cardiac awareness, but not gastrointestinal awareness, than those with other anxiety disorders. Studies 2 and 3 included a test of heart rate perception in which subjects silently counted their heart-beats without taking their pulse. In Study 2, 65 panic disorder patients showed better performance than 50 infrequent panickers, 27 patients with simple phobias, and 46 normal control subjects. No group differences were found in ability to estimate time intervals. In Study 3, 13 patients with panic disorder and 15 with generalized anxiety disorder showed better heart rate perception than 16 depressed patients.     

Ontogeny of thermoregulatory mechanisms in the rat.

The ability of rats to select a warm environment was studied as a function of postnatal age (birth to 13 days). Animals younger than 5 days demonstrated no choice response (movement to a warm compartment, 36-37 degrees C); however, they did demonstrate movement within the start compartment (23 degrees C). Increasing the motor capabilities of the pups, by injection of L-3,4 dihydroxyphenylalanine (L-dopa, 50 mg/kg), elicited a choice response in 4-5 day-old animals. Younger animals demonstrated no choice of a warm environment even though they moved considerably. Also there was no difference between L-dopa-treated and control animals in the magnitude of temperature change in pups isolated from their mother for 1 hr. The evidence suggests development of behavioral thermoregulatory mechanisms prior to abilities for internal regulation.