Introduction to Cognitive Neuroscience fmri results in context. Doug Schultz

Transcription

1 Introduction to Cognitive Neuroscience fmri results in context Doug Schultz

2 Overview In-depth look at some examples of fmri results Fusiform face area (Kanwisher et al., 1997) Subsequent memory effect (Brewer et al., 1998) (Wagner et al., 1998) Extinction learning (Phelps et al., 2004)

3 How do we localize brain function using fmri? Is there a cortical region specifically involved in face perception?

4 Hypothesis Where in the brain would you look for a region specific to perceiving faces?

5 Visual processing streams Where? What?

6 Background Face recognition may rely on different brain areas than object recognition Single unit recordings in macques Implanted electrodes in epilepsy patients Damage in occipitotemporal regions impairs face recognition fmri studies show larger responses to faces than objects Other possible explanations

7 Experimental design Part I - Identify regions that respond to faces Part II Faces vs. scrambled faces, faces vs houses Part III Different orientation faces vs hands, 1-back task with faces and hands

8 Part I 20 participants, 5 removed for excessive motion Six 30s blocks Each block had 45 stimuli (each presented for 670ms) Between each block was 20s of fixation Two runs of the task, results averaged

9 Part I results

10 Part I results cont.

11 Experimental design Part I - Identify regions that respond to faces Part II Faces vs. scrambled faces, faces vs houses Part III Different orientation faces vs hands, 1-back task with faces and hands

12 Part II Design Blocks of faces and scrambled faces Scrambled faces control for some of the lower level visual features (luminance) Blocks of faces and houses Tests if face areas are simply responding to differences between stimuli within a similar category

13 Part II Results

14 Experimental Design Part I - Identify regions that respond to faces Part II Faces vs. scrambled faces, faces vs houses Part III Different orientation faces vs hands, 1-back task with faces and hands

15 Part III Design Blocks of faces and hands Controls for face orientation and for animate vs. inanimate Blocks of faces and hands used in a 1back task Controls for potential attention differences between faces and other objects

16 One-back task Time

17 Part II Results

18 Conclusions There is a region in the fusiform gyrus FFA that responds to faces This effect is not explained by low level visual features (luminance) Effect not driven by different examples of a larger category (Faces v Houses) Effect not explained by animate vs inanimate or faces capturing more attention

19 Other explanations? Think of another possible explanation that would explain the data Expertise? Involvement in emotion?

20 How do we remember events? Application of event-related designs

21 Memory encoding background Left PFC is involved in semantic processing during encoding When semantic processes are interrupted, activity in the PFC and memory are decreased ERP results show that remembered words evoke a different type of activity than non-remembered words Medial temporal lobe seems to be important based on lesion data, but not consistently detected with fmri

22 Block vs Event Related Designs Block designs average across a number of consecutive trials Event-related designs allow researchers to identify individual events and average across some variable of interest

23 Experimental Design I Block design Participants are exposed to word lists that are either semantically encoded (abstract or concrete) or non-semantically encoded (uppercase or lowercase) Periods of fixation between word list blocks

24 Experimental Design I Mini-example below IfIfthe theword wordisislowercase concrete raise your right hand, if it isisabstract uppercase raise raise your your left left hand hand HONEST PENCIL talent truck bird TRUST love TREE

25 Results I Block design Words vs fixation Block design Semantic vs nonsemantic Event-related Words vs fixation

26 Experimental Design II Words are intermixed with fixations and participants are performing semantic encoding Listen to this word list and answer if the word is concrete or abstract (don t write anything)

27 Experiment Design II Number 1-24 on a piece of paper Do you remember the word? How confident are you (high/low)? Now we would specifically look at the words you recognized (high confidence) and compare brain activity on the encoding trials for those words and compare it to the encoding trials when you didn t remember the word

28 Results II

29 Results II

30 Conclusions Increased activity in PFC and parahippocampal gyrus at encoding predicts better memory Extensive semantic processing in PFC may organize these details in WM and pass that information to parahippocampal gyrus

31 More subsequent memory Convergent results from another group using picture stimuli

32 How can we use fmri to answer questions about specific neural circuits? Are findings with human subjects consistent with those from non-human animal models?

33 Extinction learning

34 Neural circuit supporting extinction Homberg, 2012

35 Experimental Design Acquisition Extinction Training Day 1 Extinction Test Day 2

36 Results

37 Results Orange = CS+ > CSBlue = CS+ < CS-

38 Results A. Amygdala activity greater during acquisition than during extinction B. Timecourse of CS+ response during acquisition (red) and extinction (yellow) C. During extinction the degree of amygdala activity is correlated to the magnitude of the fear response

39 Results A. Subgenual ACC responses during the experiment B. During extinction test (Day 2) the activity of the subgenual ACC is correlated to the magnitude of the fear response

40 Conclusions fmri can be used to test hypotheses about the neural circuitry supporting a particular phenomenon Subgenual ACC appears to be involved in the extinction of fear responses (consistent with non-human animal studies) Impact of instructions/expectations? Interpretation of fmri signal decreases

41 Take-home messages fmri is a powerful tool Non-intrusive method to examine many parts of the brain Good spatial resolution, not great temporal resolution Results should be interpreted carefully It is important to use appropriate procedures for the question being asked Contrasts and comparisons are critical