[Biology Class Notes] on Amygdala Pdf

The limbic system holds the power to record and remember life events. And as every event has favourable and unfavourable aspects, they trigger various emotions in us. By the virtue of this quality, the limbic system is hence responsible for the regulation and stimulation of human emotions. The three main components of this system include the amygdala brain, hippocampus, and hypothalamus. 

Together these structures profoundly influence our reasoning and judgements and eventually our behaviour at an unconscious level. The proceeding sections cover the cover aspects of the amygdala brain that affect us in our everyday lives.

How to Define Amygdala?

The amygdala is a part of the limbic system that controls flight and fight responses of the body. It is well regarded as the emotional centre of the brain. In simple words, we can define amygdala as a small brain structure of grey matter in the temporal lobe of the brain, which works to regulate our emotions and motivations.

Amygdala Location

Amygdala is located in the temporal lobe of the brain. It is located just in the front of the hippocampus, in the middle of the lobes. It is in proximity to the cingulate gyrus as well. Thus, finding the amygdala location is not as complex as it may seem.

Amygdala Structure

The amygdala is best described as almond-shaped, implying that it is oval in shape and has ends that are a bit pointed. It is a subcortical brain that consists of 13 complex nuclei and grey matter. It is best defined as a cluster of nuclei. It is more scientifically preferred to be called an amygdaloid nucleus.

Amygdala Function

It wasn’t until the 19th century that the amygdala was discovered. Several investigations are being carried out to know how the parts of the amygdala function. Nonetheless, several successive examinations show that the amygdala has the following functions:-

• Evaluating the Emotional Value of Events: The amygdala determines whether any event was happy, sad, frustrating, etc. It has the ability to discern impending dangers and works on preparing the body to meet the demands of the situation. Hence, it plays an inextricable role in our judgement.

• Learning: It is the amygdala that facilitates learning on the paradigms of negative or positive reinforcements.

• Amygdala and Hippocampus: Since it is adjacent to the hippocampus, which stores episodic memory, the amygdala can incur changes or modifications on the memory through emotions. It can also trigger emotions through reminiscing on random objects. This can be positively used to enhance memory.

To put it in simple words, the emotional aspects of the amygdala facilitate the attachment of emotions to the episodic memory of the hippocampus. This is a classic way in which the amygdala and hippocampus are often found to be working together.

Parts of the Brain – Amygdala Pathway

Each amygdaloid nucleus receives input and sends output to multiple but distinct brain regions. These inputs and outputs are referred to as pathways, and they can be afferent or efferent depending on whether they are received or sent.

 

Afferent Projections –

The dorsal and medial thalamus, as well as many cortical areas such as the insula, prefrontal cortex, parahippocampal cortex, and temporal cortex, send impulses to the basolateral group of nuclei. It also receives a large number of neural fibres from the brainstem.

In any case, it is clear that all of these fibres transmit a broad range of somatosensory, visual, and optical information to the amygdala. Because it receives a large number of afferent fibres, the basolateral group of nuclei is also known as the amygdaloid zone of sensory convergence.

All of the impulses received by the basolateral group are projected to the centromedial group, where they are supposed to be arranged and then sent to various motor centres to stimulate a response to the received information. As a result, the central group is also known as the amygdaloid zone of motor divergence.

These are the Structures That Send Fibres to the Amygdala in Particular:

• Olfactory bulb

• Orbitofrontal cortex

• Cingulate gyrus

• Basal forebrain

• Medial thalamus

• Hypothalamus

• Brainstem

 

Efferent Projections –

The primary function of the amygdala, as previously stated, is to modulate the activity of the hypothalamus. It accomplishes this through two major pathways: the stria terminalis and the ventral amygdalofugal pathway.

The Stria Terminalis: This pathway connects the amygdala’s centromedial nucleus to the hypothalamus’s ventromedial nucleus. The pathway also transports fibres to the brain’s septal nuclei and thalamic regions.

In addition to efferent fibres, the stria terminalis transports fibres from these three areas back to the amygdala. Stria terminalis is important in the stress responses of many different types of organisms.

Amygdalofugal Pathway: This is the amygdala’s primary efferent pathway. It originates in the amygdaloid complex’s centromedial and basolateral nuclei and transports fibres to various locations throughout the nervous system.

The basolateral group’s axons travel medially through the innominate substance, terminating in the hypothalamus and septal nuclei. It is known that innominate substance sends cholinergic neurons to the cortex of the brain, which is important for social behaviour modulation.

What Happens When the Amygdala Part of the Brain Obtains Damage?

The amygdala is responsible for sensing dangers and threats. Additionally, it is associated with memory and emotions. Thus damage to this part of the brain can profoundly send our lives in disarray. Some of the changes that the damage can incur are:

• The intensity of emotions increases drastically.

• Inability to recognise the emotion or feel it

• Depression, stress or anxiety.

• Irregular eating habits, which are bizarre or on the extremes.

• Loss of perception such as object recognition

• Memory loss.

• Excessive need for stimuli. 

Our mental health can bring significant changes in the amygdala. Studies have found that PTSD, depression, anxiety can cause changes in the structure of this part of the body.

Fun Facts

Amygdala has a multinuclear part of the brain. It has a total of 13 nuclei. The complex amygdala part of the brain was not found until the 19th century. And when it was discovered by the renowned Burdach in the year 1952, it was only thought to be just a little body of grey matter in the mammalian temporal lobe. 

Later it was called the amygdaloid nucleus. However, today, despite thousands if not lakhs of research, neuroscientists can’t claim to have known it fully. Amygdala continues to be an enigma to date. It is this complexity of the amygdala that is often referred to as the amygdala brain.