Cognitive Neuroscience Lecture 3: Cognitive Neuroscience Methods

Where is the "seat of the mind"?

* Is it the heart? The ventricles? People didn't used to know.
* **Phrenology:** different functions localized to different regions
	+ looked at size of the bumps on skull to deduce which areas are highly developed in an individual

Against phrenology: anti-localizationist

* **Fluorens** destroyed parts of pigeon brain and noticed that many faculties affected by one part, and that they recovered; concluded that all parts are capable of all functions
* This was evidence for the **aggregate field theory**: all sensations, all perceptions and all volitions occupy the same seat in the cerebral organs. The faculty of sensation, percept and volition is then essentially one faculty
* Noticed that many functions affected by removing parts

Big debate: **Localization** (specific function maps to specific part) **vs. equipotentiality** (all parts of brain are capable of all functions)

* skull palpators (phrenology/localization) vs. bird-brain ablators (Fluorens/equipotentiality)
* Phrenology is a case study in bad science (pseudoscience), but the idea of localization of function is important
* They really just needed the right methods to study! Namely...
* **Neurology and neuropsychology**: looking at diseased/damaged brain

**Modern Neuropsychology**

* **John Hughlings Jackson**: noticed characteristic progression of seizures, which led him to propose a topographic organization in cerebral cortex (e.g. map of body)
	+ his logic was that if a seizure progresses in a particular way across the body, a

later
confirmed to be true

less
extreme type of localization

o
localization
of *symptoms or behavior,*  not *function*

o
based
on interconnectedness of brain areas

Claude
Bernard: same mentality; you need to look at the body as a whole

**Paul Broca:** patient could comprehend speech but
not produce

“tan,
tan, tan, tan”

Left
inferior frontal lobe damage: Broca’s area

**Carl Wernicke**: patient could produce speech
(fluent aphasia), but not comprehend

Nonsensical
speech

Cannot
understand written language

“I
called my mother on the television and did not understand the door…”

Left
posterior temporal/parietal region

**Broca’s area**: speech production

**Wernicke’s area**: language comprehension

Double
dissociation: language comprehension and speech production are dissociated;
selective impairment in one but not other

Causes of
neurological/neuropsychological problems:

vascular
disorders: stroke, hemorrhage

o
tissue
supplied by damaged artery dies

Tumor:
usually in white matter

Degenerative
disorders:

o
Alzheimer’s
(plaques and tangles)

§  Above average brain volume shrinkage

§  Especially shrinkage in hippocampus
(hippocampus—memory)

§  Brain generation should develop
treatments because Alzheimer’s is 3x cost of other elderly diseases

o
Parkinson’s
(loss of dopamine neurons)

§  Loss of coordination

o
Huntington’s
(basal ganglia atrophy)

o
Pick’s
(fronto-temporal atrophy)

§  Difficulty in speech/thinking

§  Personality change

Viral
infection, nutritional deficiency

o
AIDS
destroys white matter

Studying
Patients with brain lesions

Look
at diseased/damaged brains

Assess
mental abilities through cognitive testing

Attempts
to link *specific* cognitive deficits
to damage in *specific* brain regions

If
a specific brain region contributes to a particular cognitive task, then a
lesion in that area should impair performance of that task

Example:
Is \_\_\_\_\_\_ function dependent on the same brain structure as \_\_\_\_\_\_\_\_\_ function?

**Single dissociations**: Patient A can do Task X but not Y

o
E.g.
can name something using smell but not sight

Problem
with single dissociation: one task may be more sensitive than the other task
because of difficulty/sensitivity

For
example, a task that measures something might need more concentration than the
other task

o
Performance
may just reflect generalized concentration problem in patients, not
specifically what you’re looking for (memory, familiarity, etc)

o
Performance
may be bad because you’re looking at patients, a group likely to already have
trouble with difficult or concentration-requiring tasks

**Double dissociations**: Patient A can do Task X but not Y

Patient B can do Task Y but not X

o
Perform
2 memory tests; you don’t need them to be in the correct order.

o
Then,
you’ve controlled for any cognitive setback that is generalized to all
neurological patients (e.g. difficulty with concentration)

Why double dissoc?
Consider the following single dissoc:

Damage A à can’t read à conclude that A critical for reading

Is it that they just can’t read,
or is it a broad perceptual problem? Maybe A is not just for reading, but for
perception in general. You can check whether it is just for perception in
general by doing other perceptual tasks, but that will only show that A is not
specific to reading…it won’t show what IS specific to reading. So if you do
something where a person with damage A can, let’s say, recognize images
(another perceptual task) but not read, then you’ve shown that A is not just
generally for perception, but is for reading specifically.

Advantages
& Disadvantages of studying Patients with Brain Lesions

Advantages:

Natural
experiment

Suggests
causal role for brain area in particular cognitive function

Double
dissociations provide strong evidence for separable processes

o
E.g.
Broca’s vs. Wernicke’s, production vs. comprehension

Disadvantages:

Somebody
gets brain damage

Not
controlled experiment

Damage
not always localized; many functions can be impaired

Damage
not same from person to person

Plasticity,
recovery, connections to other regions (dynamic processes you can’t control)

Cognitive
Neuroscience Methods

Disruption methods: **what function does certain region have**

Isolate
brain area with disruption

Brain
disruption implies cognitive disruption

Measure
task performance

Determine
which cognitive function is supported by the disrupted brain area

They
cannot do \_\_\_\_\_\_\_\_ when \_\_\_\_\_ region is disrupted

Recording
methods: **what area lets me do certain**
task

Isolate
a cognitive function through task selection (task involves \_\_\_\_\_ cognitive
function)

Engage
the brain in that function

Measure
the brain activity while it is performing that function

Determine
which brain area supports the targeted cognitive function

They
must use \_\_\_\_\_\_ region in order to do \_\_\_\_\_\_

Cognitive
Psychology

Study
of mental activity as an information processing problem

Cognitive
psychology theories refer to hypothetical mechanisms: underlying mental
processes and representations

Try
to measure in terms of % or reaction time. Why?

Because
we want to know WHAT FACTORS CHANGE how fast or accurate you are, and we want
to CONTROL them

o
Measure/control
1 variable at a time

Testing
mental representations from behavioral methods

Letter
matching-task: press if two letters are from same category (vowel/consonant) or
different

Different
response time: degree of mental processing required to perform the
letter-matching task

Identical
(e.g. AA or aa) has faster response time than just same letter (e.g. Aa)

o
This
implies that letters are represented with physical identity, not just phonetic

Disruption
Methods

Permanent
lesions

Temporary
disruption

o
Pharmacology

o
Cortical
stimulation

o
TMS
(trans-cranial magnetic stimulation)

Cortical
stimulation: Case study AA

Experienced
seizures at age 9

Tumor
discovered and removed

Seizures
and tumor returned at 16

**Cortical stimulation undertaken prior**
to tumor resection

Subdural
electrode array placed on cortex surface

Allows
for **recording** (to identify epileptic
focus) and **stimulation**

Stimulation
can produce **disruption of cognitive**
processes **supported by underlying neural tissue**

o
This
is used by surgeons to limit cognitive impact of surgery (feedback as they go
along)

Research
as well: cortical stim can help understand brain-cognition relationships

o

o
What is the empirical logic? What
assumptions must we make?

o
Logic:
disrupted region controls impaired task.

o
Assumption:
we assume that the task impairment is not a result of a generalized impairment
in concentration or other larger cognitive ability that is disrupted in all
surgical patients. This is a single dissociation study, not double
dissociation, so we have not controlled for it being a neurosurgical patient.

Procedure
on each trial:

o
Stim
and non-stim trials mixed

o
Stim
and non-stim don’t feel different

o
On
each trial: some amt of electricity for 5 sec

o
Stim
presented 1 sec into period

o
Asked
to respond ASAP

Results: lower percent correct during stim of region A

Can you make the conclusion that A is the multiplication
center?

o
No, because it could be necessary for number recognition.

Empirical logic: cortical stimulation can produce disruption
of cognitive processes subserved by underlying neural tissue

o
This does not mean that this tissue is solely responsible for
that process

o
I would want to see him do addition and other tasks with
numbers, as well as letters to remove confounding variables

o
Conclusion that it is the “multiplication center” is
unwarranted because it could be for memorization, symbol recognition

o

Additional data provided was language production, picture
naming, reading aloud, responding to commands, all of which got above 90%. Also, stim on that area affected
math, stim on other areas did not

o
This implies that it really is math related…but I’d still
want to see more about numbers

The
challenge in Cognitive Neuroscience

To
learn about brain/cognition, we ask participants to perform tasks

But
a task typically involves *multiple*
cognitive functions/mental operations

We
are interested in identifying the neural substrates of specific cognitive
functions, not the entire task

Challenge: isolating a specific function from within a complex task

Doing both of these
processes would isolate multiplication from addition

We
do experiment with stim and no stim and in each, test multiplication and
addition, and measure response time and % correct in each

**TMS (trans-cranial magnetic**
stimulation): Disruption method

Magnetic
stimulation can disrupt normal activity of the brain, creating a “virtual
lesion”

Magnetic field outside the skull induces electric field inside skull

o
Tight
wire coil insulated

o
Electrical
current thru coil

o
Magnetic
field generated that goes through skin, scalp and generates current

o
Neurons
fire

MRI
can be used to display cortical area targeted

Direct
effects are about 1-1.5 cm^3

o
Activation
restricted to this size

There
are different coil types, and different induced fields

Single
pulse or repetitive TMS (rTMS)

rTMS:
longer lasting effect, used in research and also effective as a therapy for
depression

if
a TMS is placed over the hand area of the motor cortex, muscles of the wrist
and fingers will be activated

o
twitches

o
participant
knows it’s involuntary

subject
begins counting and then Broca’s area (left) is stim

when
people temporarily given a pulse, they failed to identify what they were
supposed to identify

it
takes time to perceive and analyze letter.

o
Same
response time as if it was destroyed

TMS advantages

higher
spatial resolution than neuropsych

changes
neural activity in a spherical area of 1 cm^3

high
temporal resolution

o
when
the pulse follows the stimulus by a certain amt of time, participant fails to
ID stim on large % of trials

can
be used repeatedly

provides
info about *causal role* of brain area
in particular perceptual/cognitive/motor function

non-invasive

TMS disadvantages

restricted
to brain regions close to the skull

difficult
to hold the coil in place

has
induced seizures in some epileptic patients

Recording
brain activity

invasive,
measure electrical activity

o
single
cell recording in animal

non-invasive,
measure blood flow or electrical activity

o
PET
(positron emission tomography)

o
fMRI
(functional magnetic resonance imaging)

o
ERP
(event related potentials)

o
MEG
(magneto-encephalography)

Single or
multi unit recording in animal

Measure
the **firing rate** of a single cell by
inserting an electrode either inside a cell or just outside (intra or
extracellular)

Determine
which experimental manipulations produce a consistent change in the baseline
response rate of cell

If
cell is responsive to some stim characteristics and not others, the inference
is that the cell is involved in the representation/processing of that feature

Receptive
field

While
activity of single cell is monitored, monkey is required to maintain fixation
(possibly anesthetize; cats)

Bar
of light is presented at various positions in FoV until stim and location are
found that produce a response in the neuron being recorded

**Receptive field**: the location over which the
stimulation affects the response of the neuron

More
of stim in receptive field = more firing

Advantages
of single/multi unit recording in animal

Single
cells can be highly selective in terms of response

Very
high temporal and spatial res

Newer
multi-unit recording techniques allow researchers to record from several
hundred cells simultaneously

Disadvantages
of single/multiunit recording in animal

Invasive

Fishing
expedition: cannot test all possibilities, so your choice of what to test
limits possible outcomes of experiments

Sampling
a very small percentage of neurons

Provides
info about relationship between task and neuronal activity but not about causal
role of neuron in cognitive task (i.e. we don’t know what would happen without
this type of neuron, just that this neuron exhibits activity under certain
conditions)