Brain: Internal and External Worlds

The Internal and External Worlds of Our Brain

The brain is an organ, but it is not an isolated organ. It is connected in various ways with the other organs of the body. This vital fact about the brain and how it works is all too often overlooked, especially by people who like to think of the brain as something analogous to a computer.

In a nutshell, the brain is connected to two “worlds”: the world within us, the internal milieu of the body; and the world outside us, the external environment. In a profound sense, the principal task of the brain is to mediate this divide – to mediate between the vital requirements of the internal milieu of the body (the vegetative functions) and the ever-changing world around us, which is the source of everything our bodies need but is indifferent to those needs (with the exception of our parents – especially during childhood – and other loved ones, who for that very reason occupy a special place in the mental economy).

The vegetative nervous system performs the task of keeping the body alive from moment to moment, controlling heart rate, breathing, digestion, temperature, and so forth. To perform these functions, the body requires, and actually consumes, material from the outside world – principally food, water, and oxygen. It also requires a suitable ambient temperature, as the organs of the body can only function within a very narrow temperature range. The same applies to sexual needs – though sexual “consummation” is necessary for the survival of our species as a whole rather than of each one of us individually. In short, to maintain and sustain the visceral jellyfish that we all have inside us, the internal world of the body has to interact in an appropriate way with the external world around us and make the world meet its needs, and it is the brain that manages this difficult task. When the external world no longer meets our many needs (when the brain is no longer able to regulate the inner functions of our bodies, by virtue of its interactions with the external world), we die – of hunger, thirst, suffocation, heatstroke, or one of the many other hazards that constantly threaten the integrity of the internal world of the body.

This point is obvious, and clearly irrevocable. How, then, does the brain perform these vital functions? In a broad sense, to begin with, we can address a narrower question: How is the brain linked, anatomically and physiologically, with the inner and outer world of the body?

It is important to remember that the action system always operates in concert with the perceptual systems, the primary function of which is to guide action. Photo by Elena.

Perceiving and representing the external world

The brain is connected to the outside world in two main ways. The first is through the sensory apparatus (the organs of vision, hearing, etc.); the second is through the motor apparatus (the so-called musculoskeletal system). This is how we receive information from the world and how we act on the world.

The essential facts are that sensation is generated by specialized sensory receptors (in the eye, ear, etc.), that transform selected physical features of the environment into nerve impulses and send the resultant information to the brain. In the case of vision, cells in the retina send (most, but not all) visual information, via part of the thalamus, to the back of the occipital lobes. A similar arrangement applies to hearing, in which case (most, but not all) auditory information is transmitted (via a different part of the thalamus) to the superior surface of the temporal lobe. In the case of somatic sensation (touch, pain, etc.), the relevant information is sent from the surfaces and joints of the body to (mainly) the anterior part of the parietal lobe. Many people refer to somatic sensation as the sense of “touch”. In fact, touch is part of a group of different sensory modalities that transmit several types of information from the surfaces of the body, of which tactile sensation is only one. There is also vibration sense, temperature sense, pain sense, and muscle- and joint-position sense. Each of these could be regarded as a sense modality in its own right, in that each is served by a specific type of receptor and projects separately to the brain. However, all these sense modalities send information to a roughly similar location in the brain, in the parietal lobe, which forms the basis of the body schema, and they are therefore grouped together as “somatic sensation”.

It is important to be aware that the modality of somatic sensation carries only part of the information about the state of the body to the brain – that is, information about the external aspect of the body., the “musculoskeletal” part, which is in contact with the outer world. We need to know about pain and temperature in the outside world in order to act on it. Information about the internal world, relating to the viscera, is not conveyed by sensors such as those for touch, pain, and do forth.

The two remaining sensory modalities – taste and smell – are “chemical” in nature. Taste is closely connected to somatic sensation in the tongue and is represented mainly in the cortex of the insula. Smell is connected to a range of structures inside the temporal lobe, including some parts of the limbic system.

The internal world

Until very recently, there was far less investigation of neuropsychological matters pertaining to the second aspect of reality – the influence of the inner world of the body on our mental life.

The internal milieu refers to the world of respiration, digestion, blood pressure, temperature control, sexual reproduction, and the like. These organs are responsible for the body's survival and in most cases loss of their functions would mean a rapid end to the life of the organism.

Information travels up through the spinal cord (and in other ways) from the interior of the body. This information reaches, in the first instance, the hypothalamus – which is the controlling mechanism (or “head ganglion”) of the autonomic nervous system (the system that controls the self-regulation aspects of the body). The hypothalamus is intimately connected with the group of structures known as the limbic system. One could say (using the language employed above in relation to external perceptions and action) that the functions of the internal milieu are “projected” onto the hypothalamus. The hypothalamus relays this information to a range of other structures throughout the limbic system and rest of the brain. In this way, the prevailing state of the body is linked with concurrent objects in the external world, and these links (which are of crucial importance for survival) are committed to memory.

Alongside the “perceptual” aspect of this internally directed system, there is also a “motor” component. There are two classes of action performed by this system. One influences the visceral milieu itself (via secretory discharges, vasomotor changes, etc.) These influences are mediated by the autonomic nervous system. But the visceral brain influences external action too. External action is mediated by the motor systems already discussed above, but, unlike voluntary action, the visceral brain releases stereotyped motor patterns, executed under compulsive pressure. This is the basis of instinctual behaviors and the expression of the emotions. Unlike voluntary action, this type of motor activity is mediated primarily by the basal ganglia. However, information about the state of the internal milieu also reaches the prefrontal lobes – where it makes an important contribution to the calculations performed by the unit for the programming, regulation, and verification of action.

Over most of the last century, neuroscience studied interaction of the mind with the environment, and tremendous progress was made. Picture by Elena.

The Brain and the Inner World, Introduction to Basic Concepts. Mark Solms, Oliver Turnbull.