The human basal forebrain. Part I. An overview

Late recovery from acquired sociopathy in a boy with a left frontopolar injury

The long-term outcome of acquired sociopathy with preservation of cognition is still unknown. Here, we present the long-term outcome of a severe antisocial change in personality that followed a traumatic left frontopolar injury in a previously gentle, loving, and introverted adolescent. Nine years after the accident, antisocial behaviors gradually became sporadic, while, at the same time, the patient's sense of responsibility and care for his family increased. He became more extroverted and assertive, yet flexible enough to deal with the hardships of his poor socioeconomic background. His "new personality" was, in fact, more adjusted than ever. We argue that his late recovery reflected a conjunction of factors, especially (i) his early age, (ii) the static nature of the injury, (iii) the preservation of the ventromedial frontal cortices and related basal forebrain regions, and (iv) an unusual asymmetric representation of social cognition in the cerebral hemispheres. Our case and the case of Franz Binz indicate that social recovery is possible after gross prefrontal injuries, even when they are no longer expected to occur. It also emphasizes the importance of reporting on the long-term follow-up of brain-injured patients.

The extended neural architecture of human attachment: An fMRI coordinate-based meta-analysis of affiliative studies

Functional imaging studies and clinical evidence indicate that cortical areas relevant to social cognition are closely integrated with evolutionarily conserved basal forebrain structures and neighboring regions, enabling human attachment and affiliative emotions. The neural circuitry of human affiliation is continually being unraveled as functional magnetic resonance imaging (fMRI) becomes increasingly prevalent, with studies examining human brain responses to various attachment figures. However, previous fMRI meta-analyses on affiliative stimuli have encountered challenges, such as low statistical power and the absence of robustness measures. To address these issues, we conducted an exhaustive coordinate-based meta-analysis of 79 fMRI studies, focusing on personalized affiliative stimuli, including one's infants, family, romantic partners, and friends. We employed complementary coordinate-based analyses (Activation Likelihood Estimation and Signed Differential Mapping) and conducted a robustness analysis of the results. Findings revealed cluster convergence in cortical and subcortical structures related to reward and motivation, salience detection, social bonding, and cognition. Our study thoroughly explores the neural correlates underpinning affiliative responses, effectively overcoming the limitations noted in previous meta-analyses. It provides an extensive view of the neural substrates associated with affiliative stimuli, illuminating the intricate interaction between cortical and subcortical regions. Our findings significantly contribute to understanding the neurobiology of human affiliation, expanding the known human attachment circuitry beyond the traditional basal forebrain regions observed in other mammals to include uniquely human isocortical structures.

Developing the theory of the extended amygdala with the use of the cupric-silver technique

The amygdaloid complex is a crucial component of the basal forebrain that participates in the modulation of many homeostatic functions, emotional behaviors, and learning. These features require a widespread pattern of connections with several brain structures. In the past, the amygdaloid complex was divided into corticomedial and basolateral groups. The existence of a neuronal continuum linking the central amygdaloid nucleus to the lateral bed nucleus of stria terminalis through the subpallidal area was first revealed by José de Olmos (1932-2008) with the aid of his cupric-silver technique. This observation gave birth to the concept of the extended amygdala, a conceptual framework that is useful for understanding the anatomofunctional organization of the amygdaloid complex, with relevance for basic neuroscience and clinical interventions. Traditional tract-tracing staining methods were complicated and tedious to reproduce. Axonal terminal endings were lost among a myriad of normal fibers. The need to visualize these terminals drove de Olmos to develop cupric-silver methods that revealed disintegrating synaptic terminals, without staining normal fibers. In this article, we describe the historical events leading to the development of the cupric-silver technique that evolved into the amino-cupric-silver technique, which developed hand-in-hand over the years.

Review of the cytology and connections of the lateral habenula, an avatar of adaptive behaving

The cytology and connections of the lateral habenula (LHb) are reviewed. The habenula is first introduced, after which the cytology of the LHb is discussed mainly with reference to cell types, general topography and descriptions of subnuclei. An overview of LHb afferent connections is given followed by some details about the projections to LHb from a number of structures. An overview of lateral habenula efferent connections is given followed by some details about the projections from LHb to a number of structures. In considering the afferent and efferent connections of the LHb some attention is given to the relative validity of regarding it as a bi-partite structure featuring 'limbic' and 'pallidal' parts. The paper ends with some concluding remarks about the relative place of the LHb in adaptive behaving.

Resting state connectivity of the bed nucleus of the stria terminalis at ultra-high field

The bed nucleus of the stria terminalis (BNST), a portion of the "extended amygdala," is implicated in the pathophysiology of anxiety and addiction disorders. Its small size and connection to other small regions prevents standard imaging techniques from easily capturing it and its connectivity with confidence. Seed-based resting state functional connectivity is an established method for mapping functional connections across the brain from a region of interest. We, therefore, mapped the BNST resting state network with high spatial resolution using 7 Tesla fMRI, demonstrating the in vivo reproduction of many human BNST connections previously described only in animal research. We identify strong BNST functional connectivity in amygdala, hippocampus and thalamic subregions, caudate, periaqueductal gray, hypothalamus, and cortical areas such as the medial PFC and precuneus. This work, which demonstrates the power of ultra-high field for mapping functional connections in the human, is an important step toward elucidating cortical and subcortical regions and subregions of the BNST network.

Phasic and sustained fear in humans elicits distinct patterns of brain activity

Aversive events are typically more debilitating when they occur unpredictably than predictably. Studies in humans and animals indicate that predictable and unpredictable aversive events can induce phasic and sustained fear, respectively. Research in rodents suggests that anatomically related but distinct neural circuits may mediate phasic and sustained fear. We explored this issue in humans by examining threat predictability in three virtual reality contexts, one in which electric shocks were predictably signaled by a cue, a second in which shocks occurred unpredictably but never paired with a cue, and a third in which no shocks were delivered. Evidence of threat-induced phasic and sustained fear was presented using fear ratings and skin conductance. Utilizing recent advances in functional magnetic resonance imaging (fMRI), we were able to conduct whole-brain fMRI at relatively high spatial resolution and still have enough sensitivity to detect transient and sustained signal changes in the basal forebrain. We found that both predictable and unpredictable threat evoked transient activity in the dorsal amygdala, but that only unpredictable threat produced sustained activity in a forebrain region corresponding to the bed nucleus of the stria terminalis complex. Consistent with animal models hypothesizing a role for the cortex in generating sustained fear, sustained signal increases to unpredictable threat were also found in anterior insula and a frontoparietal cortical network associated with hypervigilance. In addition, unpredictable threat led to transient activity in the ventral amygdala-hippocampal area and pregenual anterior cingulate cortex, as well as transient activation and subsequent deactivation of subgenual anterior cingulate cortex, limbic structures that have been implicated in the regulation of emotional behavior and stress responses. In line with basic findings in rodents, these results provide evidence that phasic and sustained fear in humans may manifest similar signs of distress, but appear to be associated with different patterns of neural activity in the human basal forebrain.

Heterogeneous dopamine populations project to specific subregions of the primate amygdala

Amygdala dysfunction has been reported among patients with various psychiatric disorders, and dopamine is critical to the amygdala's ability to mediate fear conditioning. Recent work indicates that the midbrain dopaminergic neurons have heterogeneous receptor and membrane channel profiles, as well as differential physiologic responses to discrete stimuli. To begin understanding how dopamine affects amygdala physiology and pathology in higher primates, we mapped the inputs from the midbrain dopaminergic neurons to various amygdala nuclei in the monkey using retrograde and anterograde tracing techniques, and single and double immunofluorescence histochemistry for tracer and tyrosine hydroxylase, a dopamine marker. Our results show that the primate amygdala as a whole receives broad input, mostly from the dorsal tier of the substantia nigra, pars compacta, and the A8-retrorubral field. Input from the A10-ventral tegmental area, while present, was less prominent. These results differ from data in the rat, where the midline A10-ventral tegmental area is a major source of dopamine to the amygdala "mesolimbic" pathway. Both the "amygdala proper" and the "extended amygdala" receive the majority of their input from the dorsal tier of the substantia nigra and A8-retrorubral field, but the extended amygdala receives additional modest input from the ventral tier. In addition, the "extended amygdala" structures have a denser input than the "amygdala proper," with the exception of the lateral core of the central nucleus, which receives no input. Our anterograde studies confirm these findings, and revealed fine, diffuse terminal fibers in the amygdala proper, but a denser network of fibers in the extended amygdala outside the lateral core of the central nucleus. These results indicate that the entire extent of the dorsal tier beyond the A10-ventral tegmental area may regulate the amygdala in primates, and subsequently serve as a source of dysfunction in primate psychopathology.

Amygdala projections to central amygdaloid nucleus subdivisions and transition zones in the primate

In rats and primates, the central nucleus of the amygdala (CeN) is most known for its role in responses to fear stimuli. Recent evidence also shows that the CeN is required for directing attention and behaviors when the salience of competing stimuli is in flux. To examine how information flows through this key output region of the primate amygdala, we first placed small injections of retrograde tracers into the subdivisions of the central nucleus in Old world primates, and examined inputs from specific amygdaloid nuclei. The amygdalostriatal area and interstitial nucleus of the posterior limb of the anterior commissure (IPAC) were distinguished from the CeN using histochemical markers, and projections to these regions were also described. As expected, the basal nucleus and accessory basal nucleus are the main afferent connections of the central nucleus and transition zones. The medial subdivision of the central nucleus (CeM) receives a significantly stronger input from all regions compared to the lateral core subdivision (CeLcn). The corticoamygdaloid transition zone (a zone of confluence of the medial parvicellular basal nucleus, paralaminar nucleus, and the sulcal periamygdaloid cortex) provides the main input to the CeLcn. The IPAC and amygdalostriatal area can be divided in medial and lateral subregions, and receive input from the basal and accessory basal nucleus, with differential inputs according to subdivision. The piriform cortex and lateral nucleus, two important sensory interfaces, send projections to the transition zones. In sum, the CeM receives broad inputs from the entire amygdala, whereas the CeLcn receives more restricted inputs from the relatively undifferentiated corticoamygdaloid transition region. Like the CeN, the transition zones receive most of their input from the basal nucleus and accessory basal nucleus, however, inputs from the piriform cortex and lateral nucleus, and a lack of input from the parvicellular accessory basal nucleus, are distinguishing afferent features.

Corticotropin-releasing hormone neurons in hypertensive patients are activated in the hypothalamus but not in the brainstem

The corticotrophin-releasing hormone (CRH)-expressing neurons were studied in the hypothalamus and brainstem of individuals who suffered from essential hypertension and had died due to acute myocardial infarction or brain hemorrhage. Healthy normotensive individuals who died in accidents made up the control group. In hypertensive patients we found extremely high expression of CRH in all parts of the hypothalamic paraventricular nucleus (Pa). In addition, CRH neuronal profiles were observed in the caudal hypothalamic area and dorsal parts of the extended amygdala. In the control group, CRH neurons were found only in the Pa and in much smaller numbers than in hypertensive patients. Also, in contrast to the controls, we found in hypertensives a very high number of CRH fibers running from the most rostral part of the Pa to the median eminence and innervating the caudal part of the suprachiasmatic nucleus (SCh). A quantitative evaluation showed that the area covered by CRH fibers in the SCh of hypertensives was about three times larger than that in the control SCh. Linear regression analysis demonstrated a negative correlation between the area of CRH fibers and the number of vasopressin (VP) or neurotensin (NT) neurons within the SCh. This relationship occurred particularly in hypertensive patients in whose SCh a larger CRH fiber area and a smaller number of VP or NT neurons were observed. We found a few CRH neuronal profiles and fibers in brainstem nuclei that are involved in cardiovascular regulation, but no apparent difference was observed between the control and hypertensive group.

Monoaminergic innervation of the macaque extended amygdala

The extended amygdala is a group of structures including the central and medial amygdaloid nuclei, bed nucleus of the stria terminalis, and sublenticular substantia innominata. This group of structures is thought to be important in a variety of psychiatric disorders, many of which are linked in one way or another to monoamines and their transporters. However, not much is known about the distribution of these molecules in the primate extended amygdala. Thus, we mapped the distribution of fibers immunoreactive for tyrosine hydroxylase, dopamine beta-hydroxylase, serotonin, dopamine transporter, and serotonin transporter in the brains of macaque monkeys. Tyrosine hydroxylase-, serotonin-, and serotonin transporter-immunoreactive fibers were found in highest concentrations in the lateral division of the central nucleus and lateral dorsal part of the bed nucleus of the stria terminalis. Dopamine beta-hydroxylase-immunoreactive fibers were found in the highest concentration in the lateral ventral bed nucleus of the stria terminalis. Dopamine transporter-immunoreactive fibers were found in the highest concentrations in the lateral juxtacapsular and lateral dorsal capsular subnuclei of the bed nucleus and lateral capsular subnucleus of the central amygdaloid nucleus, though in much lower amounts than was present in the striatum. These results suggest prominent roles for these transmitters, particularly in the lateral dorsal bed nucleus and lateral part of the central nucleus. The relative absence of dopamine transporter in the extended amygdala suggests that this transmitter acts more through volume transmission while serotonin, which is generally accompanied by proportionate amounts of transporter, may act more like a classical neurotransmitter. In addition, the finding of heavy concentrations of dopamine- and serotonin-immunoreactive fibers in the lateral central nucleus and lateral dorsal bed nucleus lends further support to the idea of these areas as parallels in some respects to the striatum.