The central nervous system is formed by the brain and spinal cord. The brain in turn contains the cerebrum, cerebellum and brainstem.

The cerebrum is the largest part of the brain and plays a central role in the control of most bodily functions, including awareness, movements, sensations, thoughts, speech, and memory. 

The cerebral cortex, the outer layer of grey matter of the cerebrum, is found only in mammals. In larger mammals, including humans, the surface of the cerebral cortex has depressions, called sulcus, which allows considerable increase in surface area without much increase in volume.

The convolutions of the cortex give it a wormy appearance. Each convolution is delimited by two sulci and is also called a gyrus (gyri in plural). The cerebrum is divided into two halves, known as the right and left hemispheres. A mass of fibers called the corpus callosum links the hemispheres. The right hemisphere controls voluntary limb movements on the left side of the body, and the left hemisphere controls voluntary limb movements on the right side of the body. Almost every person has one dominant hemisphere. Each hemisphere is divided into four lobes, or areas, which are interconnected:

  • The frontal lobes are located in the front of the brain and are responsible for voluntary movement and, via their connections with other lobes, participate in the execution of sequential tasks; speech output; organizational skills; judgment; and certain aspects of behavior, mood, and memory.
  • The parietal lobes are located behind the frontal lobes and in front of the occipital lobes. They process sensory information such as temperature, pain, taste, and touch. In addition, the processing includes information about numbers, attentiveness to the position of one’s body parts, the space around one’s body, and one’s relationship to this space.
  • The temporal lobes are located on each side of the brain. They process memory and auditory information and speech and language functions.
  • The occipital lobes are located at the back of the brain. They receive and process visual information.

Specific parts of the cerebral cortex receive inputs from multiple areas, integrate the incoming sensory information, and also form connections between sensory and motor areas. Because they are involved in organizing information that comes from various other areas of the brain, they are linked to complex functions, which are known as associative cortical functions or higher cortical functions. 

Associative cortical functions:

  • Attention
  • Memory
  • Orientation
  • Calculation
  • Perception
  • Language
  • Motor planning (praxia)
  • Executive functions (Behavior)

Dementia affects all of the cortical function in different combinations and degrees, MEMORY is always compromised. 

Brain structures related to memory:

Memory is the ability to acquire, store and recall information. The acquisition stage is learning in the same way that evocation is the remembering stage. There are so many and diverse memories that each one has stored in the brain, that this makes the existence of two equal people practically impossible. Thus, the basis of individuality lies in memory. The set of memories of an individual is an important part of his personality. Memories aren’t stored in just one part of the brain. Different types of memory are stored across different, interconnected brain regions.

Types of memory:

  1.     Long term memory: events are stored persistently and can remain for many years. Long term memory is consolidated by hippocampus activity. 

The long-term memory can be subdivided in:

  • Implicit memory: memorized knowledge cannot be described in a conscious manner. In this case, we find the memorization of the motor sequences that allow us to perform tasks such as swimming or cycling, which we learn and execute automatically and unconsciously (procedural). It can also result from priming, which occurs when a previous experience or exposure to one stimulus affects the way your brain responds when exposed to another stimulus. For example, in word-judging tasks, participants identify pairs of associated words such as BREAD–BUTTER faster than non-associated pairs such as BREAD–DOCTOR. Implicit memories rely on the basal ganglia and the cerebellum.
  • Explicit memory: memorized knowledge can be described by means of words or other symbols, such as when we mention the year we were born, the name of a friend or the states of our country (semantic). It can also be episodic, when it stores information regarding events and their context, such as what the event was, and where and when it occurred. Three important areas of the brain are involved in explicit memory: The hippocampus, the neocortex and the amygdala.
  1. Short term memory: enables the brain to remember a small amount of information for a short period of time. The shortest type of memory is known as working memory, which can last just seconds; It allows information to be retained long enough to follow a reasoning, understand and answer a question, memorize what has just been read, memorize a phone number long enough to enter it. This type of memory is organized by the prefrontal cortex and leaves no file.

Relevance of the Hippocampus

The hippocampus is primarily responsible for our ability to learn and remember. It sits deep inside our brain and is the switch point that decides whether experiences or what we have learned are stored. This area is also called ´Tor to Erinnerung´. Most fascinating is that the hippocampus is the only region of the brain where new nerve cells can be formed. Unfortunately, not all of these young nerve cells survive, they need a lot of support in the early phases to have the chance to become fully functional nerve cells after weeks or months. The cells that help the neurons survive and are, so to speak, the nursing and care personnel are called glial cells. Glial cells provide suitable nutrition and clean the environment of the nerve cells. However, glial cells in turn have to have a healthy environment and can only perform perfect “care work” for the nerve cells if they also experience good conditions. Therefore, healthy sleep  and a  healthy, nutrient-rich diet  are of immense importance, so that this particular brain region can regenerate. (“The hippocampus has a ‘self-healing programme’ which we must activate or which should not be hindered by our way of life” – Praxis Dr. Karner).

But of course, it is the totality of positive stimuli that causes nerve cells to develop and grow: sufficient physical activity, meaning in life, social contacts and mindfulness (avoidance of permanent stress).

But on the other hand, the hippocampus can even shrink due to an unfavourable lifestyle: permanent stress, anxiety, depression, overweight and untreated diabetes, and even lack of exercise and nutrition with processed products and few nutrients. Each of these negative risk factors is associated with a smaller hippocampus and an increased risk for Alzheimer’s disease. A larger hippocampus with well supplied nerve cells can therefore protect us from Alzheimer’s dementia and can help to ensure that we are still mentally fit at an advanced age. Prevention is also an essential factor here!

Quelle: Blausen.com staff (2014). “Medical gallery of Blausen Medical 2014” ( CC BY 3.0)

The hippocampus is the first region damaged by dementia (as in Alzheimer’ s disease) usually followed by regions in the cerebral cortex. This of course also impairs the regeneration of nerve cells. As long as only the hippocampus is affected, there is hope that self-healing can still be initiated, but as soon as other brain regions are affected, this will no longer be possible and there can only be a hope of stopping the progression of dementia. This of course means that it is extremely important to diagnose as early as possible in order to stop the damage or, in the best case, reverse it.

References:

  1. Fotuhi, M., Do, D. and Jack, C. (2012) ‘Modifiable factors that alter the size of the hippocampus with ageing’, Nature Reviews Neurology. Nature Publishing Group, 8(4), pp. 189–202. doi: 10.1038/nrneurol.2012.27.
    https://www.ncbi.nlm.nih.gov/pubmed/22410582
  2. Varma, V. R. et al. (2015) ‘Low-intensity daily walking activity is associated with hippocampal volume in older adults’, Hippocampus, 25(5), pp. 605–615. doi: 10.1002/hipo.22397.
    https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4425252/
  3. Raji, C. A. et al. (2014) ‘Regular Fish Consumption and Age-Related Brain Gray Matter Loss’, American Journal of Preventive Medicine, 47(4), pp. 444–451. doi: 10.1016/j.amepre.2014.05.037.
    https://www.ncbi.nlm.nih.gov/pubmed/25084680
  4. Euston DR, Gruber AJ, McNaughton BL. The role of medial prefrontal cortex in memory and decision making. Neuron. 2012;76(6):1057-1070. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3562704
  5. Queensland brain institute website https://qbi.uq.edu.au/brain-basics/memory/types-memory
  6. Angelo Machado, Neuroanatomia funcional– 3rd edition Atheneu 2013
  7. Bradley’s Neurology in Clinical Practice. 7th edition Elsevier LTD, Oxford– 2015