emotion

Fear and the amygdala

Posted on by Iasmina Livia Hornoiu

What is fear? Why are we sometimes afraid? Can fear be inhibited? What produces fear – the brain or the heart?

It is definitely the brain! More exactly, something in the brain – a tiny, almond-shaped structure, which sits anteriorly to the hippocampus, called the amygdala. This small part of our brain is to blame for  the perception of fearful stimuli and the physiological responses (increased heart rate, electrodermal responses etc.) to fearful stimuli.

As part of the FEAR system, the amygdala connects to the medial hypothalamus and the dorsal periaqueductal grey matter (in the midbrain), which is important in pain modulation in the dorsal horn of the spinal cord, as well as to sensory and association cortices. The lateral nucleus of the amygdala receives inputs from different brain regions, thus allowing the formation of associations, required for aversive conditioning. Following the processing in the lateral nucleus, information about the stimulus is, then, projected to the central nucleus of the amygdala, where an appropriate response to the stimuli is initiated, provided that the stimuli are detected as threatening or potentially dangerous.

The amygdala is involved in emotional learning and memory, modulating implicit learning, explicit memory, attention, social responses, emotion inhibition and vigilance.

You can find the article on memory here, to brush up a bit.

  • Implicit memory is a type of learning, which cannot be voluntarily reported or remembered. It includes the memories for skills and habits, for procedural knowledge, grammar and languages, priming, simple forms of associative learning and classical conditioning. The latter is particularly important for fear. It involved a conditioned stimulus (CS) and an unconditioned, painful/fearful stimulus (US), with US preceding CS and determining a fearful response to CS. This type of fear learning is adaptive and is known as sensitisation or acquisition.

There are two different pathways in the amygdala, important for fear conditioning. The “low road” pathway: sensory information projects to the thalamus, which directly communicates with the amygdala; this pathway is fast, modulating rapid responses of the amygdala to different types of fearful stimuli. The “high road” pathway is an indirect pathway: sensory information projects to the thalamus and from there, it is conveyed to the sensory cortex for a finer analysis; the sensory cortex, then, communicates the processed information to the amygdala. This pathway ensures that the sensory stimulus is the conditioned stimulus. So the responses of amygdala to threatening stimuli are both rapid and sure.

  • Explicit memory refers to the memory of facts and events; in the case of fear is means the processing and retention for a long time, of emotional events and information. For this type of fear learning, the amygdala interacts with the hippocampus. There is a distinction between the formation of memory for aversive experience (fear conditioning), which is based on previous experience, and explicit learning (in the hippocampus), which involves learning and remembering aversive properties of different threatening stimuli. The memory in the hippocampus is enhanced by arousal produced in the amygdala. The activation of the amygdala can make different cortical areas, not just the hippocampus, more receptive to stimuli that are adaptively important, thus ensuring that unattended, but important stimuli gain access to consciousness.
  • Social responses involve the ability to recognise a stimulus as good, bad, neutral or arousing. This ability, however, does not depend on the amygdala. There is one exception here, otherwise we wouldn’t be talking about it in the context of fear mediated by amygdala – fearful facial expressions. According to Darwin, social species, like humans, use facial expressions to detect internal emotional states of other members of the group. This function, mediated by the amygdala, is crucial in the emotional regulation of human social behaviour. Damage to amygdala has been demonstrated to result in impairment of the patient to identify fearful faces correctly and, therefore, react to them, accordingly. It should also be noted there is no need for the subject’s awareness of the fearful stimulus, for the amygdala to respond. In other words, when a fearful facial expression is presented subliminally, the amygdala will still show activation.
  • Inhibition of fear – it is actually very difficult to escape your own fears, as fear proves to be resistant to voluntary control. However, there is a process called extinction, a method of classical conditioning, where a CS previously associated with an aversive US in presented alone for a number of times, until the CS no longer signals the fearful stimulus. If the US is presented again, after the passage of time, it will evoke fear responses, but in different brain areas. So, the learned fear has been retained in memory, but extinction learning eliminates the response to fear. This mechanism of extinction relies on the activity of NMDA glutamate (excitatory) receptors in the amygdala. When these receptors are blocked, extinction is inhibited (so you will react to fearful stimuli) and when they are active, extinction is augmented (you no longer respond to aversive stimuli).
  • Vigilance – the amygdala is not necessary for the conscious experience of emotional states, but it plays a major role in increasing the vigilance of cortical response systems to emotional stimuli.

Memories about fearful events, just like other types of long-term memory, become permanent through a process of gene expression and novel protein synthesis, which is known as consolidation. Upon retrieval, the memories become susceptible to change and alteration, before they are reconsolidated, which involves additional protein synthesis.

The fact that humans (and probably other animals as well, I am sure, although not widely proven) have the ability to distinguish between emotional information and unemotional information is regarded as an evolutionary advantage. Emotional stimuli signal dangers and the ability to detect and appropriately react to them increases the chance of survival. However, exacerbated fear is detrimental to the individual who experiences it and is a sign of pathology. For instance, in atypical monopolar depression, which includes anxiety as one of the main symptoms, the amygdala is overactive and it determined lowering the threshold for emotional activation and abnormal reactions to stressful stimuli. A similar pattern can be seen as a result of partial chronic sleep deprivation or complete acute sleep deprivation.

References

 Beatty, 2001. The Human Brain – Essentials of Behavioural Neuroscience, Sage Publications Ltd., pg. 293-296

Bernard et al., 2007. Cognition, Brain and Consciousness – Introduction to Cognitive Neuroscience. 1st edition. Elsevier Ltd., pg. 373-383

Gazzaniga et al., 2002. Cognitive Neuroscience – The Biology of Mind. 2nd edition. W.W Norton & Company, Inc., pg. 553-572

Image by  Saya Lohovska. You can find her arts page here.

Emotions and the brain

Posted on by Iasmina Livia Hornoiu

Once upon a time, I promised I was going to write an article about how emotions affect our decision-making and why it is actually important not to ignore the feelings we have in certain situations…For several, unexplainable reasons I kept postponing this idea, and for that I am very sorry. Having said that, there is no better way of making up for this than to finally keep my promise. So, here we go!

I think I should start off with a small mention: emotions and feelings are distinct things, according to neuroscientist Joseph LeDoux. As he well puts it: “…feelings are what happen when we become consciously aware that our brain is reacting to some significant stimulus,” while it is possible that some brain structures, such as the amygdala “respond to emotional stimuli without the organism being aware of the stimulus.”

In order to achieve a better understanding of what the process of forming emotions involves, scientists talk about emotional experience and emotional expression. The latter refers to body manifestations and behaviours in response to certain stimuli, for example changes in facial expression, heart rate, sweating, skin conductance etc. It has been a subject of debate for several decades whether emotional experience or emotional response is the one responsible for formation of the other, or that they act independently. It is now believed that different emotions depend on specific parts of the brain and are determined by different neural circuits.

But why should we care about emotions in the first place? Some of you might find it strange, but emotions are intensely interconnected with reasoning and decision-making. And no, I don’t mean that they impair the process of making the right decision, it’s actually quite the opposite: most of the times we need emotions in order to be able to do what is best for us in a certain situation.

An interesting case: Phineas Gage 

A man who has gone down in history for surviving a terrible accident at the work place, but maybe mostly because of his importance in understanding the role of emotions in decision-making, is a late 19th century foreman, Phineas Gage. He had been hired as a foreman on a railroad construction site in Vermont and one of his tasks was to sprinkle explosive powder into blasting holes. This sounds like a dangerous thing to do, but Gage was regarded as one of the best people in this field: he was said to be very efficient, energetic, balance-minded, tenacious, a smart and successful business man etc.

One moment of carelessness dramatically changed his life forever, and at the same time had a huge impact on the way scientists began to think of emotions. The powder exploded and a tamping iron entered Gage’s head under his left eye, passing through his left frontal lobe, and exited the skull, leaving a hole which measured more than 9 cm in diameter.

Gage survived, but he “was no longer Gage”, as his friends and acquaintances used to say. Apart from losing vision in his left eye, the man had no motor or sensory deficits, he could hear, touch, sense, walk and talk. It was his personality that was completely changed. He became capricious, irreverent, impatient, and behaved as if he did could not predict, nor care about any professional or personal failure. He was soon fired and found different jobs over time, most of which were related to the accident and the iron rod, which had turned him into some sort of freak.

Some explanations and brain functions

The limbic system is probably the first to come to mind if you refer to brain areas involved in emotions. It consists of structures around the thalamus or in the temporal lobe, such as the amygdala, the hypothalamus, the limbic cortex, the cingulate gyrus, the fornix, the corpus callosum etc. Each one of these structures is involved in specific types of emotion and in triggering certain behaviours or responses through the autonomic nervous system. For example, the amygdala is linked to fear and aggression. Different regions (nuclei) in the amygdala are associated certain functions, so that both emotional expression and experience require the amygdala in order to be formed. Projections from amygdala are sent to the hypothalamus, which determines the autonomic response, the brain stem for behavioural reaction and the cerebral cortex, which is involved in emotional experience. The amygdala is also thought to play a role in enhanced emotional memory.

Regulation of specific emotional behaviours depending on the limbic system is facilitated by one of the major neurotransmitters, serotonine. Neurones containing serotonin originate in the brain stem (in the Raphe nuclei) and send projections to the hypothalamus. Serotonine is associated with a decrease in aggressive behaviour, but at the same time is involved in dominance, as proven by studies in rhesus monkeys.

The Papez Circuit (named after the neurologist James Papez who came up with the idea of an “emotional system”) is composed of interconnected anatomical structures (many of which are part of the limbic system) that link emotional expression and emotional experience together. Papez proposed that the cingulate cortex determines emotional experience, while the major structure involved in emotional expression is the hypothalamus. 

Below I have inserted a diagram showing the Papez Circuit, based on information from Bear et al. Note that the hippocampus is now thought to have less importance in the process of emotion formation.

The Papez Circuit

The discussion above does not fully explain what happened in the case of Phineas Gage. There is much more to emotion than that! Given the fact that the iron rod severely affected Gage’s frontal lobe, we should definitely focus our attention on this structure, too. The frontal lobe and the prefrontal cortices are involved in planning, reasoning, social behaviour, motivation, defining our personalities etc. Damage to these regions, especially to the ventromedial prefrontal cortices, results in decision-making impairment. While the intelligence and the other body functions remain intact, the patient who has suffered the damage is no longer able to exhibit normal social behaviour. The patient becomes emotionless and this lack of emotions and self motivation makes them incapable of making the right decisions.

If instead of the ventromedial prefrontal cortices, another region of the prefrontal cortices is affected, there is a very strong possibility that the patient’s intellectual abilities are compromised, along with their ability to form emotions. This region is called the dorsolateral prefrontal cortices. The person with a damage in this brain area would encounter severe difficulties when it comes to operations on numbers, words, space etc.

Another brain structure involved in the process of emotion forming is located in the right hemisphere. If the somatosensory cortices of this area are injured, the result would be similar to what can be seen in the case of a damaged ventral prefrontal cortex, but there is something more…the processes of basic body singling are also disrupted. This can be observed in patients suffering from anosognosia, a disease in which the patient is unaware and denies their disability.

I have tried to comprise a lot of information and simplify things as much as possible. If you managed to get here with both eyes open, I couldn’t be happier. Hopefully, you can see now why we should also “think with our hearts” when we need to decide about a certain situation…because the “heart” is somewhere in the brain and it knows better than us what we need to do.

For further information:

Antonio Damasio,1995. Decartes’ Error. Vintage Books

Bear et al., 2006. Neuroscience – Exploring the Brain. s.l.:Lippincott Williams & Wilknins pp. 564-581

Article about Phineas Gage

Image by Isuru Priyaranga 

Yourself…and decision-making!

Posted on by Iasmina Livia Hornoiu

I recently came across a very interesting post on Facebook, written in Romanian. This post especially caught my attention first of all because it had been made by a group very dear to me, Yourself; secondly, the topic was exactly the one I was thinking about for my next article. It’s about the role of emotions in decision-making. To be honest, this is something I’ve been studying for a while and I’ve been struggling to synthesise the main ideas for an article. But this post had it all: it is clear, concise, easy to read and definitely not boring.

I now have a very good starting point for my article. So in the meantime, I thought, why not translate it? 🙂

“When we were small it was easy to write letters to Santa, because we knew exactly what we wanted and we made choices with no difficulty. But as we grew older, things got a bit more complicated; the further we navigate the path to maturity and complexity of life, the more it becomes a challenge to make up our minds.

Why is it sometimes so hard to make choices?; Why do we get anxious and agitated whenever we have to face the impossibility of making a decision? Perhaps it comes down to the fact that the process of decision-making involves many options, and taking the variables into consideration involves both reason and emotions.

The logical process of decision-making is based on determining the value of each option. We often try to rule out as many emotional aspects as possible, to detach from them, and to evaluate each alternative in a logical, almost mathematical, way.

On the other hand, decisions we make in particular emotional states, such as when we are angry or extremely happy, are said to be “in the heat of the moment”. So, which one of these two alternatives represents the best way of making a decision?

Antonio Damasio, a Neuroscience specialist, performed studies on people with deficits in the prefrontal cortex (which is responsible for decision-making, among other cognitive functions) and the cortical structures involved in generating emotions. These people would hardly make even the simplest decisions, such as choosing between fish or chicken as a meal, going shopping, taking a walk etc. He also noted that these individuals were able to reasonably evaluate the consequences of their choices and objectively analyse the alternatives, but could not or it was extremely difficult to make any decision, no matter how simple they were.

Going back to the idea of multiple variables in decision-making, emotions are part of these variables and it is important to acknowledge their role in this process. Life is full of choices and decisions, and we have to face them all. Moreover, if our decisions are based on strong moral values, we will find the necessary means to deal with any potential challenge, regardless the final choice (which we could be quite uncertain about).”

I hope you enjoyed it! 🙂

Drawing by James Dowinton

Yourself Facebook page 

Yourself website 

Smells, learning and memory

Posted on by Iasmina Livia Hornoiu

After seeing this article’s title, you might have thought: “That sounds rather boring. I mean, what is so interesting about the nose?” Perhaps the “memory” part aroused your curiosity, though. If that’s so, you might find the following reading worth having a look at, as you could discover some surprising things about the “nose”.

I’d like to begin by emphasising something important: we don’t actually smell with our noses; it’s the brain that identifies different odours through the central olfactory pathways, but we’ll get to that soon. What does happen in our nasal cavity is the activation of the olfactory receptors (a type of neurone) of the primary olfactory system, by chemical stimuli called odourants. The binding of odourants to the olfactory receptors’ cilia triggers the transduction process, which involves G-protein stimulation, formation of the cyclic AMP (cAMP) and membrane depolarisation, by the opening of ion channels (calcium, sodium and chloride). This complex signalling cascade results in a receptor potential which is then coded as an action potential (provided the receptor potential reaches a certain threshold) and then transmitted further along the receptor’s axons (remember, they are actually neurones!) The axons form the olfactory nerve, but they also group in small clusters and converge onto the two olfactory bulbs, in spherical structures known as glomeruli. Here, the axons synapse upon second-order neurones which form the olfactory tracts and finally project to the olfactory cortex (involved in the perception of smell) and to some structures in the temporal lobes, the medial dorsal nucleus (in the thalamus) and the orbitofrontal cortex. The last two are thought to play an important role in the conscious perception of smells. A pretty intricate process, isn’t it? But it is a lot more to olfaction than this!

Running parallel to the primary olfactory system is the accessory olfactory system. This has been shown to detect our favourite smelling chemicals, the pheromones. As I am sure most of you are aware of, pheromones are involved in reproductive behaviours, identifying individuals, aggression and submission recognition. Not only the type of chemical stimuli, but also the structures in the accessory olfactory system are different: the vomeronasal organ in the nasal cavity, the accessory olfactory bulb and last but not least the hypothalamus and amygdala (and hippocampus) as the final axonal targets. The amygdala and hippocampus are known for their implications in emotions and long-term memories (check out article about memory). Thus, olfaction also plays an important role in the integration of different odours in emotion processes, as well as explicit memory and associative meanings to odours.

Interestingly, each receptor cell is defined by only one receptor protein, which is encoded by a single receptor gene. These genes form the largest family of mammalian genes: 1000 in rodents, 350 in humans. The receptor cells have unique structures and are divided into different types according to their sensitivity to odours: each receptor type is activated by a single odour; nevertheless, one odour can activate many receptor types and the combination as well as the frequency, rhythmicity and temporal pattern of receptor stimulations encode for odour information.

Studies in Drosophila have shown another very important function of the olfactory processes: the associative learning. Gustatory unconditional and odour conditional signals both converge on the antennal lobe and mushroom body of the Drosophila, establishing learning efficacy of appetitive and aversive memories in classical conditioning. The release of certain catecholaminergic neurotransmitters such as dopamine and octopamine (the insect analogue of noradrenaline) are involved in the aversive and appetitive behaviours, respectively. In an incredibly revealing study, Lee Chi-Yu and his colleagues developed this topic in much more detail. I strongly recommend you have a look at it here.

As you might have guessed, given the fact that olfaction has a wide range of implications, its impairments are present in different mental diseases. Olfaction deficits or absence (anosmia) have been identified in Alzheimer’s disease and dementia, whereas olfactory hallucinations and weird smells are one of the main symptoms of schizophrenia.

Hopefully, you didn’t find this article too long or confusing. Did you find out new information about olfaction? If you have any questions or comments, please feel free to upload your posts. I’m looking forward to them as always.

For further information:

Bear et al., “Neuroscience”, third edition, Lippincott Williams & Wilkins

My friend’s article

Another very relevant article

Photo by Isuru PriyarangaÂ