The Amazing Human Brain and Human Development

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Lesson 4: Communication and Defense
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Communication and Defense

A terrified three-year old child huddles, sobbing, in a dark corner of his room after being beaten by a drunken parent for spilling milk. A colicky infant cries for eight hours, left alone, soiled and hungry, by an immature, impaired mother. A seven-year old boy watches his father beat his mother, the most recent of many terrorizing assaults this child has witnessed in his chaotic, violent household.

Terror, chaos, and threat permeate the lives of too many children. Millions of children across the globe each year have tiny pieces of their potential chipped away by fear. When fear is omnipresent, it changes the child. These powerful experiences work to literally change the brain of a frightened child. Fear inhibits exploration, fear inhibits learning, and fear inhibits opportunity.

In order to understand what is happening inside these children, we need to continue our study of the basic organizational and functional properties of the human brain. We've already covered some of the core elements of brain structure and organization that serve as a background for this lesson. Now, let's turn our attention toward some of the key features of the brain that are directly influenced by trauma, neglect, or fear.

In order to understand the traumatized child, we must first understand the fear response. The human brain has a very elaborate and important set of neural systems involved in the response to threat. The abnormal persistent activation of these systems appears to lead to many of the symptoms seen in maltreated children. We'll begin, then, by examining the key brain systems regulating the stress response.

Neurotransmitters and The Stress Response

There are many neurotransmitters involved in the stress response. Some of the most important neurotransmitters are released from clusters of extrinsic neurons.  These systems have disproportionate power to regulate human behavior, emotional functioning, and cognition. This is because these systems originate in the brainstem and have connections in virtually all brain areas. The brainstem regulates and mediates hundreds of crucial functions -- including the complexities of the stress response.

The Reticular Activating System (RAS)

The RAS originates in the brainstem and is a network of ascending, arousal-related neural systems. The RAS plays a major role in arousal, anxiety, and the modulation of limbic and cortical processing. These brainstem and midbrain monoamine systems, working together, provide the flexible and diverse functions necessary to modulate the variety of functions involved in anxiety regulation.

Locus Coeruleus

The locus coeruleus (LC) is a critical brain stem nuclei involved in initiating, maintaining, and mobilizing the total body response to threat. The LC plays a major role in determining the value of incoming sensory information, increasing in activity if the information is novel or potentially threatening. Acute stress results in an increase in LC activity. The LC plays a critical role in regulating arousal, vigilance, affect, irritability, locomotion, attention, the response to stress, sleep, and the startle response.


The hippocampus is critical to the process of learning. It takes short-term memory and converts it into long-term memory. It plays a major role in memory, including what we call episodic, declarative, and spatial learning and memory. The hippocampus also plays a key role in various activities of the autonomic nervous and neuroendocrine systems.

Stress hormones and stress-related neurotransmitter systems have the hippocampus as a target. Various hormones (e.g., cortisol) appear to alter hippocampus synapse formation, thereby causing actual changes in gross structure and size. Repeated stress inhibits the development of neurons and atrophy of the hippocampus can occur. These neurobiological changes are related to some of the problems with memory and learning found in stress-related neuropsychiatric syndromes, including post-traumatic stress disorder (PTSD).


In the recent past, the amygdala has emerged as the key brain region in the processing, interpreting, and integration of emotional functioning. The amygdala is where fear learned from past experience is permanently stored. In the same fashion that the LC plays the central role in orchestrating arousal, the amydgala plays the central role of processing afferent and efferent connections related to emotional functioning.

The amygdala receives input directly from sensory systems throughout the brain. The amygdala processes and determines the emotional value of simple sensory input, complex multisensory perceptions, and complex cognitive abstractions. The amygdala orchestrates the response to this emotional information by sending projections to brain areas involved in motor (behavioral), autonomic nervous system, and neuroendocrine areas of the CNS.


The quality and intensity of any emotion, including anxiety, is dependent upon subjective interpretation or cognitive appraisal of the given situation. How an individual cortically interprets the limbic-mediated activity (i.e., their internal state) associated with arousal plays a major role in the subjective sense of anxiety.

Kluver-Bucy syndrome, the result of damage to or surgical ablation of temporal lobes, results in loss of fear for current and previously threatening cues. The general lack of inhibition demonstrated by this syndrome suggests a loss of the capacity to recall cortically stored information related to previous threat, or to efficiently store threat-related cues from new experience.

Other areas of the cortex play a role in threat. Foremost among these are the primary and multimodal association areas, which have direct connection to the amygdala.

Coming Up

We covered an enormous span of material in this lesson. How are you doing? I expect many questions to come up from this lesson, and I cannot urge you enough to use the Message Board for them. Your questions and thoughts will undoubtedly help shed light on the subject for others in the class. I look forward to seeing them.

In the next lesson, we're going to learn how the brain stores experience and how it is changed by those experiences.


Important Neurotransmitters in the Cortex

Do you remember what a neurotransmitter is? It is the chemical that a neuron releases in order to relay information to another cell.

Important neurotransmitters in cortical regions are GABA and glycine. The capacity of benzodiazepines to alter arousal and sensitivity to threat has long been known. The principle pharmacological treatment for many anxiety disorders involves benzodiazepine treatment, targeting GABA receptor complexes.

Scientists Demonstrate Key Role of Amygdala in Emotional Memory

The site of perception of anxiety is likely to be the amygdala. In experiments with laboratory rats, scientists have determined that a rat without an amygdala has no fear of cats! When the "storage bin" for emotional information is missing, the emotion is lost.

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