Misdiagnosis of Bipolar Disorder | Psychology Today

https://www.psychologytoday.com/us/blog/bipolar-you/201402/misdiagnosis-bipolar-disorder

Misdiagnosis of Bipolar Disorder

Getting the diagnosis right when symptoms are confusing

Posted Feb 13, 2014

Across the web you'll find increasing attention being given to the identification of bipolar mood symptoms and patterns. Solid educational information is important for those who are concerned that they may have bipolar disorder.

Even the best diagnosticians find that arriving at the diagnosis is a difficult endeavor. We're not yet at a point where we have easily obtainable biologically based tests that result in a definitive diagnosis. Similarly, we're far from being able to predict the disorder based upon genetic testing.  

We're still faced with the reality of a mental health clinician sitting with a patient and relying upon clinical interview to come up with a clear picture to identify or rule out the presence of bipolar disorder. Sometimes even with extensive inquiry and careful consideration of the data obtained, clinicians still miss the bipolar diagnosis. It happens even with the most seasoned mental health professionals. I'd be dishonest if I said it's never happened to me. Longitudinal studies have shown us that the average time from initial onset of symptoms to an accurate bipolar diagnosis is ten to twelve years!

The reality is bipolar disorder is usually difficult to diagnose based on just an initial diagnostic interview with an individual. The diagnosis has to do with very broad patterns that exist over time. When meeting with a patient for the first time, all I'm really able to see is his or her behavior and mood state in the present, which excludes about 90% of the additional information that's required to ascertain the diagnosis. The acquisition of that 90% relies upon the clinician's ability to ask the right questions and the patient's ability to provide comprehensive and accurate answers. Even then, careful attention is needed before the bipolar picture can coalesce with validity. 

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Bipolar symptoms present in many different forms and patterns. Each individual brings his or her own unique stamp to the clinical picture. We see variance in symptom acuity, symptom duration and symptom manifestations. While symptoms such as elevated energy, decreased need for sleep and accelerated thinking are common to most bipolar elevated mood states, one individual's hypomania/mania may be evident through euphoria and grandiosity while the mood elevation of another may entail irritability and outbursts of anger. Still a third may manifest his or her symptoms primarily through hyper-sexuality and impulsive spending. Further compounding the diagnostic challenge is the fact that the disorder often coexists with other psychiatric diagnoses such that we get a layering or commingling of symptoms from different diagnoses. The mental health professional is then faced with sorting out what symptoms belong to what diagnoses and how the different sets of symptoms may possibly potentiate each other.  

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I find that the three diagnoses which are most often confused with bipolar disorder or potentially coexist and therefore interfere with the diagnosis are: 1) unipolar depression, 2) attention deficit-hyperactivity disorder and 3) the group of personality disorders. In this latter realm, the individuals we most often see coming in for treatment are those diagnosed with borderline and/or narcissistic personality characteristics. There are certainly other personality disorders that can come into this mix but we find that individuals with borderline/narcissistic features tend more often to seek psychotherapy. Additionally, some of the symptoms within these two personality types can easily be mistaken as belonging to the bipolar continuum (see previous Bipolar You blog: The Relationship between Narcissism and Bipolar Disorder).

So the question for the remaining discussion is: What are some of the guidelines that help us distinguish between straight depression, attention deficit-hyperactivity disorder, personality disorders and bipolar disorders?

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Let's start with the most common: unipolar depression. More often than not, bipolar disorder begins with episodes of depression. In fact, we may see adolescents go through a few years of intermittent depressive episodes during high school before they manifest the kind of mood elevation which tips the scale towards a bipolar diagnosis.

There may also be some symptoms within the overall depressive profile that can tip us off to the underlying bipolar disorder. I'm referring to things such as periods of feeling energized while also being irritable, angry and very pessimistic about life. With these people, their depressive symptoms have not flattened them out. It's more like the intense negative feelings are accompanied by a degree of agitation. These individuals may also find that their agitation interferes with their ability to get a good night's sleep. But, these small clues, in and of themselves do not rise to the level of a bipolar diagnosis. They are just features that should garner our attention and possibly alert us that there is more present than easily meets the eye.

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The next essential element is to obtain information about the broader family history of psychiatric diagnoses, and particularly bipolar disorder. If someone comes in presenting primarily with depressive symptoms but he/she has a parent, a sibling, a grandparent or even an aunt or uncle with bipolar disorder, then one has to approach the initial unipolar presentation of depression as if it may part of a broader bipolar disorder. I think of this as "bipolar brewing" where someone has the genetic predisposition but they've not yet manifested the full range of bipolar symptoms. In these instances the individual wouldn't be diagnosed with the disorder simply because of his/her genetics, but the treatment approach would likely be different than if there was no mood disorder evidence in the family background.

The other diagnostic piece that needs to be asked of almost any patient who comes into treatment is: "What is your mood and behavior like when you're feeling really good?" To take that even further, the individual should be asked, "Does your mood ever become more intense or more elevated than what you normally experience when you're in a generally good mood." You'd be surprised how often that simple line of questioning is omitted.  After all, when someone comes in seeking help and everything he or she is talking about looks like, sounds like and feels like depression, it's easy to conclude that the individual should be treated for depression and possibly even be prescribed an antidepressant. 

Here's the rub: Antidepressants, when prescribed to someone who is genetically predisposed towards bipolarity, may indeed precipitate hypomanic or manic symptoms, thus bringing about the bipolar diagnosis. We can't ever know with certainty whether that individual would have manifested bipolar symptoms if antidepressants were not prescribed.  Had the right questions been asked up-front, the same individual may have been prescribed a mood stabilizer prior to the utilization of an antidepressant and his or her progression into hypomania or mania may have been averted.

The second complicated diagnostic issue involves attention deficit-hyperactivity disorder. This is a neurologic disorder which manifests through symptoms of attention and hyperactivity. With regard to attention we see behavior such as: poor attention to detail, frequent inattention or losing focus, difficulty following through with instructions relating to tasks, chores or homework, difficulty with organizing tasks and activities, frequently losing or misplacing things and consistent forgetfulness. In relation to hyperactivity we see: difficulties sitting still, tendencies to move around or be excessively active in situations where this is inappropriate, difficulty engaging in quiet leisure activities, excessive degree of physical activity - often acting "as if driven by a motor," and excessive talking.  There is a further variation on hyperactivity including impulsivity. This can entail: tendencies to blurt out answers to questions before they have been completely asked, difficulties awaiting one's turn and tendencies to interrupt or intrude on others. Impulsivity can also entail rapidly making choices that do not reflect good judgment.  Most of the preceding symptom descriptions reflect ADHD criteria from DSM-IV TR (American Psychiatric Association).

What's complicated about the above symptom list is that many of the same ones can be present during a hypomanic or manic episode. An individual's physical energy can be so elevated that he or she can easily appear to be hyperactive. There is also such cognitive acceleration and mood intensity that an individual's memory, attention to detail, capacity to remain focused and ability to appropriately inhibit action are all impaired. So how do we distinguish these sets of symptoms that can look so similar to each other?

The first part of the answer involves an important caveat: the distinction does not readily apply to those who are diagnosed with childhood bipolar disorder as such can exert its influence just as early as does ADHD. The salient differences are that feelings of grandiosity, intense elation and/or intense anger, racing cognition and lessened need for sleep are more salient in childhood bipolar than they are in attention deficit-hyperactivity disorder. This doesn't mean there won't be any of these themes in the attention deficit-hyperactivity realm but the preceding symptom cluster will likely have a stronger presence in childhood bipolar disorder as opposed to attention deficit disorder. 

Now let's return to distinctions between attention deficit-hyperactivity disorder and bipolar disorder in adults. It's actually rather simple. The adult with bipolar disorder who did not have childhood bipolar disorder will have experienced a point of symptom onset sometime after mid to late adolescence. The implication here is that if I'm inquiring about symptom onset and the individual being assessed reports that none of his or her symptoms were present prior to some point in adolescence or early adulthood, then it's not likely that symptoms being discussed are reflective of ADHD.

A second key distinction is that many of the attention deficit-like symptoms that are typically present during elevated mood phases are absent during midrange mood and to a lesser extent, depressed mood, though sometimes depression does interfere with attention, concentration and memory so we can see what may appear as an overlap of ADHD and bipolar symptoms during depressed mood. The one obvious period of time when the attention-deficit-like symptoms are absent for the bipolar individual is during mid-range mood. This isn't the case for someone with attention deficit-hyperactivity disorder because their symptoms are part of their baseline functioning. They don't experience periods of time when their ADHD symptoms are absent. That's not to say there isn't some variability of symptom intensity, but the attention deficit individual won't have periods where attentional, focusing, organizational and impulse inhibitory functioning are perfectly normal. Keeping the above distinctions in mind, the tuned in diagnostician can usually tease out the differences between ADHD and bipolar disorder.

The differentiation of personality disorder symptoms from bipolar disorder entails two key variables, one of which is similar to the ADHD distinction. That is, if an individual struggles with personality disorder symptoms, their struggles will typically be ongoing. Similar to ADHD, there may be some variability in symptom acuity, but the individual typically won't have times where he or she is not under the influence of the psychological processes underlying the personality disorder. Individuals with personality disorders don't get to have a vacation from their personality dynamics. Conversely, the bipolar individual whose symptoms (impulsivity, hypersexuality, anger/irritability, tendencies towards idealization or devaluation, feelings of grandiosity, etc.) may look like they belong to a personality disorder diagnosis will present with enough of a difference within mid-range mood that most of the same symptoms will be absent.

The second critical distinction between the personality disorders and bipolar disorder is that all personality disorder issues manifest in relation to interpersonal relationships. The struggles which may activate strong personality disordered symptoms are almost always within the interpersonal realm. While there is some overlap here with bipolar disorder in the sense that interpersonal stresses may activate a shift in mood phase, bipolar individuals will also tell you that there are times when the onset of their symptoms, whether elevated or depressed, will seem to come out of nowhere. There is no obvious trigger or precipitant for their mood destabilization. The only reliable explanation is that there's been an endogenous shift in their brain activity and their neurochemistry.

The above discussion is by no means exhaustive regarding differential diagnostic distinctions between bipolar disorder and other psychiatric disorders that share similar symptoms. But it should give you a good sense of the kinds of issues the clinician will be looking at when trying to sort through whether one has bipolar disorder, another diagnosis or coexisting diagnoses.

I recommend that you be cautious if a mental health professional arrives at the bipolar diagnosis after only a short period of time with you or with a family member. The narrow exception here would entail someone with a strong genetic bipolar background who presents with hallmark bipolar symptoms in the absence of any other issues that may stimulate questions about comorbidity. But even here, in the name of thoroughness, diagnosticians should nonetheless be cautious about reaching conclusions prematurely.

Once a mental health professional has arrived at a valid bipolar diagnosis I feel most comfortable when the diagnosis is presented as a strong possibility along with a clear explanation of the basis upon which the conclusion has been reached. The patient should also be cautioned that the diagnosis will only be conclusively ascertained over a more extended period of time and that both patient and clinician will be looking at this together as treatment proceeds.

One last thing to keep in mind: If the diagnostic conclusion of your mental health professional doesn't ring true for you, if you do not get a thorough and detailed explanation as to why the bipolar diagnosis is likely, it is absolutely appropriate to pursue a second opinion.  

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Russ Federman, Ph.D., ABPP is in private practice in Charlottesville, VA (www.RussFederman.com). He is co-author of Facing Bipolar: The Young Adult's Guide to Dealing with Bipolar Disorder (New Harbinger Publications). www.BipolarYoungAdult.com

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https://www.verywellhealth.com/the-frontal-lobes-2488715

The Frontal Lobes and Their Function

By Peter Pressman, MD

Updated June 05, 2019

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The frontal lobes are the regions of the brain that are thought to control many of the things that make us human. In fact, this region is proportionately much larger in humans than in other animals. It also takes the longest to mature, with development extending into young adulthood.

Functions of the frontal lobes include holding onto an idea and letting this notion guide our future behavior. The frontal lobes help us set goals and tasks for ourselves, choose appropriate actions among many options, suppress unacceptable reactions and responses, and determine the relationships between objects and concepts.

There are two main divisions of the frontal lobes: the cortex and the paralimbic regions. The cortex consists of the bodies of nerve cells lying right on the brain's surface. These cells communicate with one other via long wire-like processes called axons. Some axons plunge deep into the brain, where they communicate with structures closer to the brain's core.

Among the structures closer to the center of the brain are the paralimbic regions, which are thought to be related to basic emotions, functions, and drives. This is in contrast to the cortical regions, which are thought to be more complex, and which may allow us to think. Together, the cortex and paralimbic divisions of the frontal lobes allow us to perform tasks that are central to how we think of ourselves.

Setting Tasks

Unlike animals who just respond instinctively to what is in front of them, human beings have the ability to plan in advance. To do this, we need to be able to hold information in our mind. Otherwise, we would constantly forget what we were thinking about. This holding of information, even in the face of distraction, takes place in the ventrolateral region of the prefrontal cortex. The dorsolateral region of the prefrontal cortex is then able to manipulate the gathered information to formulate a plan.

Initiating and Sustaining Activity

The structures in the middle and frontal part of the brain (medial frontal structures) are thought to drive behavior. If these areas become damaged, a person may lose all motivation to do even the simplest task. This is known as abulia or akinetic mutism in extreme cases.

Monitoring Activity

The orbitofrontal cortex decodes and anticipates the reward values of signals, objects, and choices. For example, this region may help us determine whether something is likely to hurt or harm us in the future. The medial orbitofrontal cortex is thought to respond to rewards and the lateral orbitofrontal cortex, to punishment. The region closer to the back of the brain (posterior) is more concrete—this is the part that may immediately recognize the emotional significance of a slice of chocolate cake as being tasty and desirable.

The parts of the orbitofrontal cortex that are closer to the front of the brain (anterior) deal with more abstract and symbolic rewards, like the money that can go towards buying a chocolate cake.

Emotional Regulation

The orbitofrontal cortex also shows increased activity when someone is regulating their emotions. This is inversely related to the activities in the amygdala. Damage to the orbitofrontal cortex leads to disinhibition and thoughtless behavior, as seen in the famous case of Phineas Gage.

Anticipating and Monitoring Stimuli

The anterior cingulate cortex helps keep track of signals coming both from the outside world and our own mind and body. Anything unexpected can trigger additional processing before a response is given. For example, in the famous Stroop test, a list of brightly colored words is shown. The trick is that the word "red" may be printed in the color green. Someone taking a Stroop test is told to ignore the written word and just say the color. This careful selection and focus on just one aspect of the outside world require the use of the anterior cingulate.

Responding to Change in Salience

Salience is the measure of how important and relevant a particular signal is to you at a particular time. For example, if you're hungry, a piece of chocolate cake is quite salient. After eating half the cake, your desirability of that cake changes. To determine the significance of a piece of information, the brain must rapidly integrate sensory, visceral, and autonomic signals. The salience network involves the insula and part of the frontal cortex, which helps us give things meaning.

Switching Attention

Human beings have the ability to choose what deserves our attention. That said, depending on circumstances, our attention can quickly switch between different things in our environment.

The ventral attention network includes parts of the middle and inferior frontal gyrus and the temporoparietal cortex. This helps us orient to something rapidly, even if it interrupts a goal, and lets us decide whether we should continue to focus on the new stimulus or go back to the task at hand.

Executive Control

The abilities of the frontal lobes could all be seen as contributing to what neurologists call "executive control." This signifies our capability to control our responses to our environment, rather than just react to whatever is in front of us at the moment.

The executive control allows us to filter out distractions around us. It also allows us to control what we are thinking, and shift our focus in a way so that we are not distracted by our own thoughts. Executive control over emotions allows us to regulate how we appear to others and motivate ourselves even when we are not motivated. Finally, executive control over the motor network allows us to move our eyes or reach for something.

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https://www.verywellhealth.com/the-hypothalamus-2488578

Hypothalamus Regions and Function in the Body

By Peter Pressman, MD

Updated May 14, 2019

Medically reviewed by a board-certified physician

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If the brain were a corporation, the hypothalamus would kind of be like the "utilities" department. While a lot of the credit and attention goes towards parts of the brain that communicate, create, and act, the hypothalamus is responsible for heating, water flow, and other basic things that keep the entire system running.

The basic function of the hypothalamus can be summarized with the word homeostasis, which means keeping the internal state of the body as constant as possible. The hypothalamus keeps us from being too hot, too cold, overfed, underfed, too thirsty, and so on.   

While the hypothalamus is generally responsible for keeping us in a steady state, there are times that this state needs to change. When in an immediately life-threatening situation, you may not need to think about how hungry you are. The limbic system, which is intricately involved with emotion, communicates closely with the hypothalamus, resulting in the physical changes that are associated with particular feelings. The amygdala has reciprocal connections with the hypothalamus through at least two major pathways.

Other regions of cortex, such as the orbitofrontal cortex, insula, anterior cingulate and temporal cortices also communicate with the hypothalamus.

Regions of the Hypothalamus

Like the rest of the brain, different areas of the hypothalamus perform different functions. These areas can be distinguished by their connections to the rest of the brain. For example, the hypothalamus is divided in half by fibers of a white matter tract called the fornix, which runs from the front of the hypothalamus towards the back.

The parts of the hypothalamus closer to the inside of the brain (the medial side) communicate closely with part of the amygdala through another tract called the stria terminalis. The amygdala helps to signal fear, and the medial aspect of the hypothalamus is involved with a "fight-or-flight" response, for example by limiting appetite. There's no time to rest and digest if you're about to run for your life!

The side of the hypothalamus that is closest to the outside of the brain (the lateral side) has the opposite effect on appetite. Because this area is important in stimulating appetite, lesions in this area can lead to severely decreased body weight. This area is also important in thirst, as lesions of the more frontal part can lead to decreased water intake.

The functionality of the hypothalamus is also divided from front to back. For example, anterior parts of the hypothalamus seem more involved with cooling the body off by increasing blood flow to the skin and causing sweat to be produced. The back of the hypothalamus is more involved with keeping the body warm.

In addition, the hypothalamus is responsible for regulating our natural cycle of wakefulness and sleep. The suprachiasmatic nucleus at the front of the hypothalamus serves as our internal clock, letting us know when it's bedtime. This part of the brain is connected with light-sensitive regions that adjust our internal clock to daylight.

How Does the Hypothalamus "Talk" to the Body?

The hypothalamus modulates physical responses by communicating with the body through two routes. The first route is through the autonomic nervous system. The second is through the endocrine system, meaning the secretion of hormones into the bloodstream.

Autonomic fibers primarily come from the paraventricular nucleus of the hypothalamus, but also from the dorsomedial hypothalamic nucleus and from the lateral and posterior hypothalamus. Initially, these autonomic fibers travel in a white matter path called the medial forebrain bundle. They then pass on into the dorsolateral brainstem and periaqueductal gray matter. The fibers synapse on parasympathetic nuclei in the brainstem and intermediate zone of the sacral spinal cord, and on sympathetics in the intermediolateral cell column of the thoracolumbar spinal cord.

Many autonomic nuclei in the brainstem receive inputs from the hypothalamus, such as the nucleus solitarius, noradrenergic nuclei, raphe nucleus, and pontomedullary reticular formation.

The hypothalamus also works in conjunction with the pituitary gland to control the body's endocrine system. The pituitary has the ability to secrete hormones directly into the bloodstream. This is a rare example of a place where the blood-brain barrier normally designed to keep infections from crossing into the brain is absent from the brain's architecture.

Some hormones, such as oxytocin and vasopressin, are made directly in the hypothalamus (in the paraventricular and supraoptic nuclei, for example), and secreted near the back of the pituitary. The anterior part of the pituitary contains cells that make their own hormones. These hormones are regulated by other neurological secretions which are passed down nerve fibers into a vascular plexus, where they are released by the blood. All of these hormonal secretions are regulated by negative feedback loops, meaning that the brain is able to detect when levels of the hormone are high ​and decrease production as a result.

This may seem enormously complicated, and it is. But the ultimate task of homeostasis even in the face of adversity is well worth it!

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https://www.verywellhealth.com/the-limbic-system-2488579

Functions of the Limbic System

By Peter Pressman, MD

Updated May 15, 2019

Medically reviewed by a board-certified physician

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In 1878 Paul Broca, the French neurologist famous for so-called Broca's aphasia, coined the term "le grand lobe lymbique." The term "limbus" refers to a margin or rim. Dr. Broca was referring to the structures that surround the innermost part of the brain, at the margin of the brain's center.

Meaning of the Limbic System

The meaning of the term "limbic system" has changed since Broca's time. It is still meant to include structures between the cortex and the hypothalamus and brainstem, but different specialists have included different structures as part of the limbic system. The amygdala and hippocampus are widely included, as is the olfactory cortex.  From there, however, opinions diverge as to what is considered part of the limbic system, and what is paralimbic, meaning a structure that interacts closely with the limbic system but is not truly part of it.

What Does the Limbic System Do?

The limbic system serves a variety of fundamental cognitive and emotional functions. The hippocampi, which lay on the inside edge of the temporal lobes, is essential to memory formation. The amygdalae sit on top of the front portion of each hippocampus. Each amygdala is thought to be important in processing emotion. The amygdala communicates closely with the hippocampus, which helps explain why we remember things that are more emotionally important. The amygdala also communicates closely with the hypothalamus, the area of the brain that is responsible for regulating temperature, appetite, and several other basic processes required for life.

 The hypothalamus itself is sometimes, but not always, included as part of the limbic system. Through the hypothalamus, as well as some key areas in the brainstem, the limbic system communicates with our autonomic nervous system (which regulates things like heartbeat and blood pressure), endocrine system, and the viscera (or "gut"). 

Nerve cells in the brain are organized in different fashions depending on location. The cerebral cortex is predominantly neocortical, meaning that cells exist in 6 layers. This is different from the limbic system, where cells are either arranged in fewer layers (e.g. paleocorticoid), or more jumbled (corticoid). This less complex organization of the limbic system, as well as the limbic system's control of fundamental processes of life, has led doctors to believe that the limbic structure is evolutionarily older than the cerebral cortex.

Paralimbic Structures

The paralimbic structures form a complex network with the limbic system. Examples of paralimbic structures include the cingulate gyrus, orbitofrontal cortex, temporal pole, and part of the insula. The basal forebrain, nucleus accumbens, mammillary bodies and parts of the thalamus (the anterior and mediodorsal nuclei) are also often considered paralimbic structures due to their close interaction with the limbic system. 

Each of these paralimbic structures has been connected with emotion or basic cognitive processes. The anterior cingulate gyrus, for example, has been tied to motivation and drive. The insula is connected with our ability to sense our own internal sensations (or "gut feelings"). The orbitofrontal cortex, nucleus accumbens, and basal forebrain are involved with sensations of pleasure or reward. The mammillary bodies and some thalamic nuclei are important to the formation of new memories.  

All of these pathways are intricately connected. The amygdala, for example, communicates to the orbitofrontal pathway through a white matter bundle called the uncinate fasciculus, as does the insula. The amygdala communicates to parts of the hypothalamus and cingulate through the stria terminalis, and to the brainstem and several other structures through the ventral amygdalofugal pathway. The hippocampus largely communicates through a large white matter pathway called the fornix, which curves around the ventricles of the brain towards the mammillary bodies, sending out branches to the mammillary bodies, thalamus, and cingulate along the way.

The limbic system is a heterogeneous group of structures and serves many different functions. Those functions are fundamental to how we think, feel, and respond to the world around us. 

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https://www.verywellmind.com/what-is-the-hippocampus-2795231

Hippocampus Role in the Limbic System

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The hippocampus (red), a limbic system structure, is responsible for long-term memory. Credit: Sciepro/Getty Images

The hippocampus is a small, curved formation in the brain that plays an important role in the limbic system. The hippocampus is involved in the formation of new memories and is also associated with learning and emotions.

Because the brain is lateralized and symmetrical, you actually have two hippocampi. They are located just above each ear and about an inch-and-a-half inside your head.

How Does the Hippocampus Affect Memory?

The hippocampus plays a critical role in the formation, organization, and storage of new memories as well as connecting certain sensations and emotions to these memories. Have you ever noticed how a particular scent might trigger a strong memory? It is the hippocampus that plays a role in this connection.

Research has also found that different subregions of the hippocampus itself play important roles in certain types of memory. For example, the rear part of the hippocampus is involved in the processing of spatial memories. Studies of London cab drivers have found that navigating complex mazes of big city streets is linked to the growth of the rear region of the hippocampus.

The hippocampus also plays a role in consolidating memories during sleep. Studies suggest that greater hippocampal activity during sleep following some sort of training or learning experience leads to better memory of the material the following day.

This doesn't mean that memories are themselves stored in the hippocampus for the long term. Instead, it is believed that the hippocampus acts as something of a shipping center, taking in information, registering it, and temporarily storing it before shipping it off to be filed and stored in long-term memory. Sleep is believed to play a critical role in this process.

When the Hippocampus Is Damaged

Because the hippocampus plays such an important role in the formation of new memories, damage to this part of the brain can have a serious long-term impact on certain types of memory. Damage to the hippocampus has been observed upon post-mortem analysis of the brains of individuals with amnesia. Such damage is linked to problems with forming explicit memories such as names, dates, and events.

The exact impact of damage can vary depending on which hippocampus has been affected. Research suggests that damage to the left hippocampus has an effect on the recall of verbal information while damage to the right hippocampus results in problems with visual information.

Age can also have a major impact on the functioning of the hippocampus. MRI scans of human brains have found that the human hippocampus shrinks by around 13 percent between the ages of 30 and 80. Those who experience such a loss may show significant declines in memory performance. Cell degeneration in the hippocampus has also been linked to the onset of Alzheimer's disease.

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