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Post-Mortem Examinations
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Biopsychology – Brain Imaging Techniques
In this course, Dr Gaby Pfeifer (University of Southampton) explores some of the brain imaging techniques used in psychological and neuroscientific research. In the first lecture, we think about post-mortem examinations as an early and less technologically advanced method of brain imaging. In the second lecture, we think about magnetic resonance imaging (MRI) as a more technologically advanced method of imaging brain structure. Next, we think about functional magnetic resonance imaging (fMRI) as an equivalent measure of brain function. In the fourth and final lecture, we think about electroencephalography as a more temporally accurate measure of brain activity.
Post-Mortem Examinations
In this lecture, we think about post-mortem examinations, focusing in particular on: (i) post-mortem examinations as the oldest form of brain imaging; (ii) their relatively uncommon use cases, typically limited to when a person has died under suspicious circumstances and the examination is requested for forensic reasons; (iii) the role of post-mortem examinations in scientific research by investigating the brain damage suspected to be the cause of a behaviour of interest; (iv) the practical challenges in post-mortem examinations, including extracting the brain from the dura mater and changing the brain tissue texture into a manageable one using formalin; (v) the general structure of the brain including its hemispheres, the longitudinal fissure, and its wrinkled cortex; (vi) the insights into brain region functionality that post-mortem examinations can provide, highlighting the work of Paul Broca and Carl Wernicke; (vii) the importance of finding double dissociations in neuropsychological research; (viii) some key strengths and limitations of post-mortem examinations as a brain imaging technique.
Hello, I'm Gaby Pfeifer.
00:00:06I'm a lecturer in psychology here at the
00:00:08University of Southampton and in today's video
00:00:11course, we're going to look at brain imaging techniques,
00:00:14so I will be covering three imaging techniques today.
00:00:17Firstly, we'll start out with post mortem techniques,
00:00:20then look at magnetic resonance imaging techniques and finally,
00:00:23electroencephalography or EEG for for short.
00:00:27So as they go through those techniques,
00:00:32I'm going to say a little bit about the
00:00:34technique itself and then look at the basic mechanisms
00:00:37of the technique and also the knowledge we can
00:00:40gain from the technique as well as its limitations.
00:00:43So, let's begin with brain post mortem examinations.
00:00:47Now,
00:00:51brain post mortem examinations are one of the
00:00:51oldest methods for imaging the brain.
00:00:53They've been around way before any other sophisticated
00:00:56technology has become available to image the brain.
00:01:01Now post mortem is Latin for after death,
00:01:04and so the technique involves extracting the brain from
00:01:09the skull after the person has passed away.
00:01:12Sometimes it is also referred to as brain autopsy.
00:01:16Now, brain autopsies are not routinely performed.
00:01:20They are usually performed when they are being requested for forensic reasons,
00:01:24say for example,
00:01:29to determine the cause of death in case
00:01:30the person has passed away under suspicious circumstances
00:01:33and where it is believed that an exam of the brain could give further
00:01:37clues about the cause of the death of the person.
00:01:40Another reason why they might be performed is for research and medical purposes,
00:01:45and this will also be the focus of this video.
00:01:50So in this case,
00:01:54we would usually investigate the brain of neuropsychological patients
00:01:55who have demonstrated a particular behaviour during their lifetime
00:01:59that suggests brain damage
00:02:04and by examining their brains postmortem,
00:02:08we then hope to find out more about the relationship
00:02:11between their particular behaviour and any brain damage.
00:02:14Another reason why postmortem exams might be performed is in famous cases.
00:02:19So, for example, Albert Einstein's brain has been examined to
00:02:25find out more about the relationship between his
00:02:30his brain anatomy and his high mathematical functioning.
00:02:33So, let me tell you a little bit about the basic mechanisms of postmortem techniques.
00:02:39The technique involves extracting the brain from the skull
00:02:45to allow studying the physical brain,
00:02:49so it's quite an invasive technique and is typically
00:02:52performed by a trained pathologist or a neuroanatomist.
00:02:55Now, post mortem exams are carried out as soon as possible,
00:03:01typically within 2 to 3 working days after the person's death.
00:03:05And
00:03:10the brain sits deep within the skulls
00:03:11protective, bony tissue and is further surrounded by
00:03:14a thick connective tissue called the dura mater.
00:03:17So dura mater stands for hard mother,
00:03:21and the pathologist will have to open the person's skull and
00:03:24removed the dura mater in order to get to the brain.
00:03:28In that state, the brain is pinkish looking and quite a squishy substance,
00:03:32which will have to be fixed using a certain chemical called formalin.
00:03:37So they're going to put it in this chemical to give
00:03:42it a texture that is similar to a hard rubber ball,
00:03:45and then it is ready for further
00:03:49examination of any different anatomical brain structures.
00:03:50So I have a brain here next to me, which I'm going to demonstrate.
00:03:54So this is a life size human brain model, not an actual postmortem brain,
00:04:00but a plastic brain,
00:04:05although it does show the same very similar neural anatomical structures.
00:04:06So what you can see on the brain is the entire cerebral cortex,
00:04:10and we can also nicely see the two cerebral hemispheres,
00:04:16the right and the left hemisphere.
00:04:19And there's a large gap running through those two hemispheres,
00:04:21the so called longitudinal fissure,
00:04:26and I hope you can also see how convoluted and wrinkled the cortex is.
00:04:29And if we stretched out the cortical surface,
00:04:35it would be far too big to fit into our skull.
00:04:38And so, as the brain has evolved over many thousands of years,
00:04:40it had to wrinkle up in order to fit inside the skull.
00:04:44And one further thing I'd like to show is the little cerebellum here in the back,
00:04:48which is Latin for little brain.
00:04:53So apart from the neuro anatomical insights that we gain from looking at the brain,
00:04:55we might be more interested in looking at neuropsychological patients
00:05:01and find out more about their brain behaviour relationship.
00:05:05Now there are,
00:05:09unfortunately a number of people who suffer injuries to their brains,
00:05:10such as strokes or motor accidents,
00:05:14or they might sustain sustain a neuro degenerative disorder like
00:05:16Alzheimer's disease or other types of dementia or Parkinson's disease,
00:05:21and the location of the injury and the resulting behavioural changes will
00:05:27tell us something about the function of that particular brain area.
00:05:32One example is the discovery by the French anatomist Paul Broca,
00:05:35who worked with patients who were able to comprehend language
00:05:40and had normal mental functioning,
00:05:46but were unable to speak or produce any language.
00:05:48And, following autopsy after the patient's death, Broca
00:05:53found damage that was localised in the
00:05:56brain in the person's left prefrontal cortex.
00:05:59So I'll show you where that is.
00:06:03So the left hemisphere here and this is sort of the area of the prefrontal cortex,
00:06:07and this area later became became known as Broca's area,
00:06:13named after Paul Broca,
00:06:17which we now know is involved in speech production.
00:06:21Similarly, another neuroanatomist, Carl Wernicke,
00:06:24worked with patients who were unable to comprehend language,
00:06:30but they were still able to speak.
00:06:34So following the autopsy of Wernicke's patients, he found
00:06:36that his patients had a lesion in an area further back in the brain.
00:06:40So still on the left hemisphere,
00:06:45but further back here, in an area called the temporal lobe.
00:06:47This area is now known as Wernicke's Area,
00:06:51which we now know is involved in speech comprehension.
00:06:53So
00:06:57here we have
00:06:58two complimentary but opposite patient behaviour patterns. Right?
00:07:00One patient was able to speak but not comprehend,
00:07:04and the other one was able to comprehend but not speak.
00:07:07And this, in neuropsychology, is called a double dissociation.
00:07:10That's an important finding, whereby two
00:07:18patients have opposite but complementary patterns of behaviour, here
00:07:20related to speech. Double dissociation can conclusively
00:07:24demonstrate that the two complementary functions are
00:07:28localised in different areas of the brain,
00:07:32and that is very strong evidence for a modular account of language.
00:07:35There are two modules in the brain,
00:07:40one responsible for language production and another for language comprehension.
00:07:41So let me tell you a little bit about
00:07:46the strengths and weaknesses of post mortem examinations.
00:07:49In terms of strengths,
00:07:54they've been very influential in informing theories of
00:07:55cognitive functioning such as language and memory
00:07:58via these double dissociations?
00:08:01And they're also quite powerful in establishing causal
00:08:05relationships between the impaired brain area and the patient's behaviour,
00:08:09really suggesting that the damage to a brain area causes the person's behaviour.
00:08:14Now, we need to see that with caution, right?
00:08:19We can only make such strong claims after we have tested a number of
00:08:21brains and under person's behaviour,
00:08:26and this brings me to the limitations of post mortem exams.
00:08:28They're very often based on single case studies for the reason
00:08:33that very few patients demonstrate exactly the same brain damage,
00:08:38so there's not enough patients to compare against.
00:08:42And
00:08:45it also is the case that the brain damage
00:08:46is usually not confined to one particular brain area.
00:08:48If someone has a stroke,
00:08:53it may result in a lesion that affects
00:08:55one particular brain area but also surrounding areas.
00:08:59So the patient's behaviour may therefore not
00:09:02just result from damage to Broca's area,
00:09:05but also from the surrounding brain damage.
00:09:07We're also missing out on the individual differences.
00:09:12So to what extent is the patient's behaviour
00:09:15influenced by variables other than brain damage,
00:09:18for example, by their personality by their age by their sex and so on?
00:09:21So we need a larger population sample to
00:09:26make convincing claims about the brain behaviour relationship?
00:09:28There are some ethical considerations that we
00:09:34need to take into account whether the person
00:09:36has been able to give full informed consent
00:09:39before death to allow those postmortem examinations.
00:09:41And if the person has a severe psychological disorder
00:09:46like the severe memory loss or is unconscious,
00:09:50they won't be able to give informed consent.
00:09:53So there may be ethical issues about whether
00:09:56or not we can conduct the postmortem exams.
00:09:59And then finally, the modularity I spoke about earlier.
00:10:03The assumption that brain regions represent modules with very specific,
00:10:07independent functions, seems rather simplistic.
00:10:12We now know that the brain is much more complex,
00:10:16and the functions are often widely distributed across the cortex
00:10:19and also in deeper cortical structures.
00:10:23Post mortem techniques are positive for many things have given
00:10:26us a lot of information about different cognitive theories,
00:10:31but we need other brain brain imaging techniques to
00:10:36obtain converging evidence to establish the brain behaviour relationships.
00:10:40
Cite this Lecture
APA style
Pfeifer, G. (2022, November 07). Biopsychology – Brain Imaging Techniques - Post-Mortem Examinations [Video]. MASSOLIT. https://massolit.io/courses/biopsychology-brain-imaging-techniques/post-mortem-examinations
MLA style
Pfeifer, G. "Biopsychology – Brain Imaging Techniques – Post-Mortem Examinations." MASSOLIT, uploaded by MASSOLIT, 07 Nov 2022, https://massolit.io/courses/biopsychology-brain-imaging-techniques/post-mortem-examinations