The telencephalon, referred to as the cerebral hemispheres or the cerebrum, is the largest part of the central nervous system and make-up 85% of the brain. Technically, the telencephalon depicts the anterior-most embryonic cranial section, which arrives from the prosencephalon.
The telencephalon is a reference to the forebrain development in-utero. The telencephalon and diencephalon are derivatives of the prosencephalon- an embryonic neuronal tube. The telencephalon is Greek for ‘end brain.’ This anterior-most region has the dominant growth spurt and becomes the cerebrum.
The basic structure of the telencephalon is comprised of four sections: the cerebral cortex, the basal ganglia, the limbic forebrain structures, and the olfactory system. In addition, numerous sub-divisions contribute to the cerebrum’s immense and sophisticated processes (cognitive, emotional, and behavioral).
Defining The Telencephalon
The etymology of telencephalon arises from the Greek terms ‘telos,’ which means ‘end,’ and ‘enkephalos,’ which translates to ‘brain.’ This description illustrates both the maturation phase and the human evolutionary relevance. The telencephalon is the last realized subdivision of the brain in utero. This forebrain region is the latest cranial feature to evolve.
The telencephalon is an aspect of the forebrain responsible for memory, emotion, transmitting vital data, and movement. This cranial subdivision is sophisticated and contains sizeable network divergence. It manages goal-directed behavior and motivation. Self-determined actions require the transmission of contextual data. Information that consists of experience and emotion.
Scholars, psychologists, and neurologists initially attributed four exact subdivisions to the telencephalon. This four-sectioned framework is referred to as the traditional division. However, after extensive research, the telencephalon is revealed to consist of additional sub-sections.
The neo-cortex is a significant aspect of the telencephalon. It plays an exciting role in human evolution and higher cognitive development. The neo-cortex contains pyramidal neurons. The human neo-cortex emerges at six weeks during in-utero maturation.
Pyramidal neuron, named after the shape, is a generalized term to describe excitatory glutamatergic principal cells. These neurons work with GABAergic inhibitory interneurons within cortical networks. They are tasked with information processing.
The human telencephalon with the neocortex envelops the older components of the brain. In addition, the olfactory, limbic, and motor systems project neuronal fibers deep within the cerebrum’s subcortical structures to the brainstem.
Understanding the volitive and cognitive role and the telencephalon’s network system projections from deep within the cerebrum to the thalamus and remaining relevant brainstem areas is essential. Language, unique to humans, is a complex, higher-level cognitive ability in which the telencephalon facilitates the neuronal network.
The Telencephalon Development In-Utero
The telencephalon is derived from the developmental prosencephalon. In utero, the prosencephalon comprises the diencephalon (caudal) and the telencephalon (anterior). These two derivatives comprise the forebrain. The telencephalon will, in due course, be realized as the cerebrum.
The dorsal aspect of the telencephalon, also referred to as the pallium, emerges as the cerebral cortex. Further, the ventral aspect of the telencephalon, or subpallium, becomes the basal ganglia. The subdivisions of the telencephalon are specialized according to histological and molecular criteria.
In-utero, the telencephalon appears at five weeks. Embryonic development must be observed. There are numerous medically relevant reasons to dedicate the study of the cerebrum’s in-utero maturation. In addition to diagnosing cognitive, emotional, and behavioral disorders, the inherent human capacity of the telencephalon and its neuronal tributaries is revealing and extraordinary.
The gestational maturation period of the telencephalon is characterized by cerebral cortex growth. The surface anatomy of the brain is vital to monitor as this is the steady expansion and accumulation of neurons in the sulci and gyri. This development facilitates information processing.
The human brain produces 160 billion neuronal and glial cells in-utero. Each neuron and glial cell have a distinct cellular phenotype. The specific cranial areas grow heterochronously. The realization of the brain’s development is chiefly influenced by the telencephalon- its dominant growth spurt is at 175 to 580 days following conception.
The Neural Tube’s Differentiation Process
The delineation and formation of the neuronal tube is a process. This differentiation process is realized simultaneously across various areas in the central nervous system. From a macroscopic perspective, the neuronal tube and its lumen expand and contract throughout its development phase. This process creates the chambers of the spinal cord and brain.
After five weeks of in-utero development, the emerging central nervous system is primarily a tube-shaped instance of specialized tissue called a neural tube. The progression rate of the telencephalon rapidly exceeds the other features of the central nervous system.
In utero, the anterior portion of the neuronal tube experiences radical transitions during the early phases. During the initiation period, the neuronal tube inflates into three primary vesicles: the prosencephalon (forebrain), mesencephalon (midbrain), and rhombencephalon (hindbrain).
Eventually, as the neuronal tube’s posterior end develops, the secondary bulges (the optical vesicles) broaden laterally outward from the emerging forebrain. The telencephalon extends into two symmetrical features that eventually become the cerebral hemispheres.
The Telencephalon Functions
Essentially, the telencephalic characteristics exhibit higher-level functions unique to humans. These attributes fortify human intelligence, heightening our abilities above simple survival. In addition, memory, language, and voluntary movement strengthen individual autonomy and meaning in our lives.
Memory
The hippocampus assists in memory consolidation. Case studies that detail patients who have had their hippocamps removed to treat severe epilepsy. The surgery resulted in the patient suffering anterograde amnesia and retrograde amnesia. As a result, they could not create new memories (anterograde amnesia) or recollect past ones (retrograde amnesia).
Olfaction
The olfaction bulbs (discussed more fully below) reside within the anterior-most section of the cerebrum. The olfactory area is responsible for our sense of smell. It’s directly connected to the amygdala and hippocampus. This connection explains the salient association of human experience between smell and memory.
In other mammals, the olfactory area is significantly larger than in humans. Other cranial faculties have played a more influential role in our human evolution. Therefore, our reliance on smell for survival has diminished considerably.
Language
Our ability to communicate- speech and language- is chiefly attributed to parts of the cerebral cortex, a section of the telencephalon. Particularly, the left hemisphere of the cerebrum is responsible for language and speech production.
Broca’s area, situated in the frontal lobe, regulates motor language. Wernicke’s area, in the frontal-parietal lobe, supervises speech. The arcuate fasciculus, a collection of neurons, connects Broca’s area with Wernicke’s area.
Emotion
The limbic system regulates emotions. The telencephalon consists of an extensive network that communicates with other cranial areas. Its vast communication network is an intricate part of the limbic system. The amygdala (discussed fully below) regulates fear and modulates stress. The Papez circuit, intrinsic to the limbic system, is a physiological loop tasked with cortical control.
Movement
Voluntary movement- organizing, monitoring, and execution- is managed by the motor cortex of the telencephalon. The motor cortex is found in the precentral gyrus and consists of the primary motor cortex, premotor cortex, and supplementary motor area.
Human Behavior
Human behavior’s vast spectrum is determined by the cerebrum’s intricate organization and neuronal system networking. The complex formation of the network’s organization is due to the exact, distinct, and specialized neuronal subtype consolidation in particular telencephalic cranial areas.
The development of the proliferative ventricular zones illustrates the immense complexity of the telencephalon. The brain’s precise, strategic organization results from heterogeneous progenitor cellular types.
The Telencephalon- The Cerebral Cortex
The cerebral cortex is the outermost cranial tier. It appears wrinkly due to the numerous folds caused by the gyri and sulci. The convolutions facilitate large amounts of information, creating space for more neurons. The human cortex comprises six layers, measuring 0.08 to 0.16 inches thick. It contains neurons and gray matter and is 310 square inches in volume.
One of the major responsibilities of the cerebral cortex is incorporating sensory impulses, direct motion, personality, learning, and emotion. In addition, it manages higher-level intelligence like thinking, consciousness, reasoning, problem-solving, and decision-making.
The cerebral cortex is distinct from the cerebrum and lies on the surface of the cerebrum. This exterior tier makes up approximately 50% of the brain’s total volume. Primarily, about 90% of the cerebral cortex comprises the neocortex.
The Telencephalon Subcortical Structures
The cerebral cortex is an integral part of the telencephalon. Included in the collection of telencephalic structures belonging to the cerebral cortex are the prefrontal cortex, the motor cortex, the somatosensory cortex, and the occipital cortex.
In addition to the gray matter of the cerebral cortex, the telencephalon consists of subjacent white matter. The substrate portion also has sizeable amounts of gray matter. The white matter tracts of the telencephalon include the corpus callosum, anterior commissure, and internal capsule—the corpus callosum assists with interhemispheric communication.
Along with the cerebral cortex, the telencephalon has an array of subcortical features that perform a variety of essential roles in cognitive, emotional, and behavioral processes. These include the hippocampus, amygdala, and cingulate gyrus- the limbic system, the olfactory bulbs, and the basal ganglia.
The Telencephalon- The Limbic System
The limbic system is essential for executing regular functions. It strategically aligns cognition with emotion resulting in required behavior. Responses govern these inherent strategies—for example, fight or flight reactions, reproduction, maternal care, and nutrition intake. Therefore, the limbic system of the telencephalon manages emotional and behavioral responses.
The region of the limbic system is located deep within the brain, beneath the cerebral cortex, and above the brain stem. There are specialized physiological cranial features that contribute to the overall operation of the limbic system. The limbic system is acknowledged as the ‘primitive brain’- or the ‘deep-within’ brain.
The thalamus and hypothalamus produce specialized hormones which manage thirst, hunger, and emotional temperament. The basal ganglia process reward-driven behavior, voluntary movement, mindfulness, and routine rehearsal. The hippocampus and amygdala are the principal cranial features of the limbic system.
Essentially, the limbic system is an arrangement of individualized anatomical features. These structures regulate endocrine or autonomic processes, manage responses to emotional stimuli, engage with reinforcing behavior, and organize emotion and memory. The term ‘limbic’ is derived from Latin, which means ‘rim.’
Amygdala
The amygdala is the site that is tasked with processing emotions. The etymology of amygdala is rooted in Greek, amygdale, which means almond. Therefore, the amygdala is named due to its shape and size, which is oval and small. This telencephalic structure is responsible for fight-or-flight responses.
The amygdala stimulates the adrenal gland’s release of hormones- adrenaline and cortisol. These hormones circulate within the blood and impact the body, preparing it physiologically to survive. Survival strategies include dilating air passages and facilitating oxygen flow to vital organs. Blood vessels contract, redirecting blood to the main muscle groups. Adrenaline dilates pupils, enhancing vision.
The amygdala is found in the medial temporal lobe, directly anterior to the hippocampus. The amygdala is a paired anatomical structure in each brain’s hemispheres. Acting integral to the limbic system, the amygdala is a neuronal intersection, mediating emotions and encoding memory.
Initially, the amygdala was believed to be singularly involved in fear and primitive responses to aversive stimuli. However, today the amygdala is understood to also respond to rewarding stimuli. Essentially, this neuronal interface facilitates emotional learning and memory.
The Amygdala And Emotional Valence
Emotional valence is the degree of positivity or negativity attributed to external stimuli response. The subjective quality (personal affectation) of the experienced emotion evaluates the circumstance in internal responses. Attractive stimuli elicit positive valence, and aversive stimuli provoke negative valence.
Valence describes the type of experienced emotion. Positive emotions are experienced and expressed as joy, happiness, or pleasure—negative emotions and feelings of fear, anxiety, and suffering. Affective translation of personal feelings is revealed in individual behavior and social norms. Essentially, the amygdala processes emotional valence.
The Amygdala- Psychiatric Disorders And Treatments
The amygdala is medically relevant in understanding various psychological disorders like depression, post-traumatic stress disorder, obsessive-compulsive disorder, autism, hypervigilance, phobias, addictions, and binge drinking.
Treatments for mental illness and destructive emotions surrounding the amygdala are extensive and include deep brain stimulation, cognitive behavioral therapy, transcranial magnetic stimulation, and pharmacology.
Hippocampus
The hippocampus grows from the medial pallium during week six of the embryo’s gestation period. Recognized as a telencephalic structure, the hippocampus is situated in the inner medial area of the temporal lobe.
The hippocampus is integral to the limbic system and is crucial to regulating emotional reactions. This telencephalic structure facilitates long-term memory storage. In addition, it strengthens the mind’s ability to resist forgetting.
The hippocampus resembles a curvy seahorse. An extension of the temporal lobe, this cranial feature is characteristically vulnerable and is easily affected by an array of stimuli. It’s a facet of the limbic lobe.
Olfactory Bulb
The olfactory bulbs are arranged anteroventrally. These are flat, elongated structures that are situated in the forebrain. Neuronal cells in the nasal cavity transmit aroma data to the olfactory bulbs. The axons of olfactory receptors project
The olfactory bulbs are a feature of the limbic system. When different scents arouse this area, the bulbs communicate directly to various parts of the limbic system. Generally, there is a strong connection between memories and smells.
Cingulate Gyrus
The cingulate gyrus is situated on the medial plane of the cerebral hemisphere and contributes significantly to the limbic system. Described as arch-shaped, this folding lies immediately above the corpus callosum. The front section is called the anterior cingulate gyrus/cortex (ACC).
The anterior cingulate cortex envelops the frontal area of the cingulate gyrus and transmits electrical chemical signals across to both hemispheres. In addition, the anterior cingulate cortex performs varied autonomic functions. These functions include managing heart rate, blood pressure, and various cognitive roles- empathy, emotion, reward-governed behavior, and decision-making.
The cingulate gyrus has received recent focus in neurological studies regarding memory inhibition. In addition, the anterior cingulate cortex is responsible for rendering memories stimulated by fear conditioning.
The anterior cingulate cortex has evolved considerably over the last 100 000 years. As a result, its capacity to communicate with a range of neo-cortical areas, specifically Brodmann’s area 10, has strengthened significantly.
The Telencephalon- The Basal Ganglia
The basal ganglia are an arrangement of cell masses within direct proximity of each other. This tight networking of subcortical nuclei extends from the base of the telencephalon. This multiplex shroud the striatum- which contains caudate nucleus and the putamen. In addition, the basal ganglia envelop the globus pallidus.
Chiefly, the basal ganglia manage movement execution, movement learning, behavior, emotion, and administrative functions. In addition, the basal ganglia have robust interconnections to the brain stem, thalamus, and cerebral cortex.
Conclusion
The telencephalon is a derivative of the prosencephalon. It resides in the anterior-most region of the forebrain and becomes the cerebrum. The telencephalon’s growth rate rapidly exceeds the other facets of the neuronal tube. The dominant growth determines the direction of the brain’s formation.
The telencephalon has mainly four divisions: the cerebral cortex, the basal ganglia, the limbic forebrain structures, and the olfactory system. It also consists of numerous subdivisions. The functions of the telencephalon include memory, language, behavior, emotion, and olfaction.
