How Does Our Brain Create Fear?

Why do we feel fear? For years, a part of the brain called the amygdala has been implicated in this emotional response. This region links memories with emotional responses, one of which might be fear. A patient (known as S.M.) with dysfunctional amygdalae on both sides of her brain has been known to show no fear in response to various fear-inducing stimuli, including life-threatening traumatic events.

Everyday Gas Induces Fear in the Brain

Another stimulus that is known to evoke fear is carbon dioxide. Inhaling this gas turns on a protein which in turn plays a role in fear and anxiety (how this protein works in inducing fear remains unknown). How would patients with damaged amygdalae react to this stimulus? A team of researchers at the University of Iowa tried to find out.

fear center in the brain
The first image is a scan from a normal patient and the next three are from patients with damaged amgydalae. The area marked in red shows the lesions present in their brains. [Image Source: Iowa Neurological Patient Registry at the University of Iowa]

‘Fearless’ Patients Show Fear

To their surprise, they found that the 3 people with lesion in their amygdalae (let’s call them patients) showed a greater degree of panic than a group of patients with normal amygdalae. The patients described having experienced emotions they had never felt before, with their descriptions residing well under the category of ‘fear’. Clearly, these results show that the amygdala is not an absolute necessity for fear. However, anticipatory responses to the inhalation, such as an increased heart rate before inhalation, were shown to be significantly increased in controls when compared to patients.

These results led the authors to believe that the carbon dioxide activated a previously unused pathway in patients with damaged amygdalae. One possibility is that most stimuli that normally induce fear are external—perceived visually or auditorily—, whereas inhalation of carbon dioxide represents a physiological, internal, change that does not need processing by the amygdala to generate fear. Another conclusion that the authors came to was that the amygdala might, to some degree, inhibit fear, since the degree of panic attacks was milder in the control group.

Fear is an important survival mechanism, and this experiment gives important clues to its origin. You can read about this research here.

Why Does a Nail on a Blackboard Make Us Cringe?

Why is the sound of nails on a blackboard (and to some of us, even the thought of it) enough to make us wince and cover our ears? Do our ears respond differently to them?

It has been previously known (by brain imaging studies) that in addition to the auditory part of our brain (the auditory cortex), the emotional center of the brain—the amygdala—is also activated by unpleasant sounds. Now how does this dual response work? How are unpleasant sounds represented in the brain? Do specific auditory signals go to the amygdala from the auditory cortex or does it receive them directly? Researchers at Newcastle University have performed a series of experiments seeking to determine precisely this.

The brain scans of 16 participants were obtained in response to a variety of pleasant (bubbling walter, a baby laughing) and unpleasant sounds (a fork scraping glass, nails against a blackboard). Based on these scans, the research team could chalk out the series of events that lead to the disturbed response exhibited upon hearing unpleasant sounds.

Why this aversion to some sounds? [Image Credit:]

The sound signals are first processed by the cortex and then transferred to the amygdala. The amygdala, upon recognizing the signal as being ‘unpleasant’, kicks in to transfer a signal back to the auditory cortex, driving it to perceive the sound as even more unpleasant. What this means is that the intense discomfort you experience when you hear an electric drill is driven by an emotional response. “It appears there is something very primitive kicking in,” says Dr Sukhbinder Kumar, the paper’s author from Newcastle University. “It’s a possible distress signal from the amygdala to the auditory cortex.”

The authors also noted that most sounds we classify as unpleasant belong to a high frequency range of the auditory spectrum, the same range in which the sound of a human screaming can be found. Perhaps our aversion to these sounds are thus evolutionary.

This study could be extended to learn more about the generality of this result. Is this specific to unpleasant sounds? What about words with negative connotations? What about words that are merely ‘negative’ but not distinctly unpleasant? The same research methodology can be extended to uncover the mechanisms by which our brain processes auditory information.

You can read about this research here.

Have Excellent Autobiographical Memory? Your Brain is Differently Wired.

Do you remember what happened on the 6th June, 1999? Or 19 September 2000? Well, if you can effortlessly reel off the answers, and in general recollect events in your life with remarkable accuracy, you don’t just have good memory—you’d be pleased to know that you have what is called “Highly Superior Autobiographical Memory”.

This is a newly described ability of individuals to recall events from their personal past, including the days and dates of occurrence, with high accuracy. People with strong memories don’t necessarily have HSAM. They use certain mnemonics and strategies to perfect the art of memory, and this often doesn’t extend to autobiographical memories. In a case of one of the most famous mnemonists, the patient described living his life “in a haze”. Conversely, intense rehearsal of memories does not seem to be the primary means by which people with HSAM store their rich repertoire of memories.

Having excellent autobiographical memory could be a result of your brain being structured differently. [Image Credit:]
Having excellent autobiographical memory could be a result of your brain being structured differently. [Image Credit:]

How Are they “Highly Superior”?

Researchers at the University of California, Irvine tried to see if this difference between high autobiographical memory and good memory was also reflected in the way these are stored in the brain. They recruited people who claimed to have extremely good autobiographical memories and performed routine memorization tests on them. They identified 11 people who had vastly superior abilities to remember events in their past. However, these people performed no better than normal individuals on these tests. Yet when it came to public or private events that occurred after age 10½, “they were remarkably better at recalling the details of their lives,” said McGaugh, senior author on the new work.

They found that HSAM participants also had obsessive tendencies, though it remains unclear if the two are linked, and if so, how. Furthermore, they found that the brains of these participants were anatomically different from the brains of normal participants in 9 structures. Using MRI, some of these regions are shown to be active while autobiographical memories are being recalled.

Cause or Effect?

It must be noted, however, that these structural differences could either be a cause of HSAM or an effect. Our brains are remarkably plastic and embody the saying ‘we are what we do’. The wiring of our brains is subject to change upon repeated patterns of activity. Thus, the difference in certain brain regions of people with HSAM could simply arise as a result of different thought patterns in these people. Either way, this research does give us more information about the intricate workings of the brain and how it resolves the details of the world we live in.

You can read about this work here. It was published in the journal Neuroscience.