# Presentation: 683350

## Behavioral models of impulsivity in humans and non-humans: Individual differences and effects of drugs. 

- Harriet de Wit
- The University of Chicago
- Jerry Richards
- University of Buffalo (SUNY)

**Notes:**
-plan to talk about the concept of impulsivity, its measurement in the laboratory and its relation to drug abuse

## Impulsivity closely linked with drug abuse

- As a determinant
- _Individual differences_: risk factor
- Momentary changes
- As a consequence
- _Acute drug effects_
- Chronic drug effects

## Impulsive Symptoms in Psychiatry:Common but Heterogeneous 

- * failure to consider consequences; aggression (Antisocial Personality Disorder)
- * engaging in behaviors with damaging consequences (e.g., excessive spending, drug use) (Borderline Personality, Substance Use Disorder)
- * distractibility, difficulty waiting, lack of inhibitory control (ADHD)
- * impaired judgment, risk-taking (Substance-Induced Disorder)

**Notes:**
-here impulsivity is seen more as a failure to plan ahead, and a tendency to, act without consideration of negative consequences

## Two broad types of impulsivity

- _Cognitive impulsivity_
- Insensitivity to delayed consequences
- Lack of planning, lack of forethought
- _Behavioral inhibition_
- Difficulty inhibiting prepotent responses
- Difficulty suppressing unwanted behavior, resisting temptation
- Difficulty waiting

**Notes:**
- over the years, many attempts have been made to develop a laboratory measure of impulsivity, especially in ADHD children
- the first 2 measure rapid and careless performance of tasks, but these are confounded by intelligence
- #3 measures tendency to engage in socially unacceptable behaviors (grabbing, cutting into line, lack of social judgment)
- #4  involve inability to inhibit motoric actions
- #5 most common,widely used, most well-developed in the lab delay of gratification

## Procedures to Measure Impulsivity

- Cognitive
- _Delay discounting_
- Risk taking

- Behavioral inhibition
- _Stop Task_
- Go/no-go
- Delay of gratification

## Data to be presented

- Individual differences
- Effects of drugs
- Humans
- Rats and mice

## I.  Delay Discounting 

- preference for immediate rewards over larger delayed rewards
- partying instead of studying
- spending money now instead of saving

**Notes:**
-it is not known whether each of the behavioral indicators of impulsivity just described are related to a single underlying process or whether they represent different processes
- this important question can be addressed by developing sensitive behavioral tests thought to assess each of them.
- operational definition related to resistance to temptation and delay of gratification
- this definition is framed in simple operant terms, readily quantifiable

## Reward Discounting as a Function of Delay

**Reward Discounting as a Function of Delay**

- 0

- short

- Delay

- $10

- Current Value

-  Steeper discount function is an index of impulsive decision-		making.

- long

## Individual Differences in Delay Discounting

- • psychiatric patients (Crean et al, 2000)
- • gamblers (Petry, 2001)
- • drug users (Bickel, 1999; Mitchell, 1999)
- • variability among healthy volunteers
- • Relationship to personality

## Healthy _x0008_Volunteers: Distribution of 

**Healthy _x0008_Volunteers****: ****Distribution of**** **
**Delay Discounting Log K values** (N=165)

**0**

**5**

**10**

**15**

**20**

**25**

**30**

**35**

**40**

**45**

**50**

**Frequency**

- -.5

- -1

- -1.5

- -2

- -2.5

- -3

- -3.5

- Log K

## Healthy volunteers: Low positive correlations between delay discounting and personality

- Barratt Impulsivity Scale (N=184)
- Cognitive Complexity (r=.19, p=.01; ‘I [do not] save regularly’, ‘I am more interested in the present than future’)
- Nonplanning (‘I say things without thinking’; r=.15, p<.05)
- Multiphasic Personality Inventory (N=125)
- Negative Emotionality (r=.19, p<.05; I am nervous, tense, easily upset, alienated)

## Rat

**0**

**50**

**100**

**150**

**Value  (******** L of  Water)**

**0**

**4**

**8**

**12**

**16**

**Delay to water delivery (sec)**

**Rat**

**0**

**120**

**240**

**360**

**0**

**2**

**4**

**6**

**8**

**10**

**Value ($)**

**Delay to receive $10 **
**(days)**

**Human**

**Delay discounting in humans and rats**

## Individual differences in delay discounting in rats:  Relationship to novelty responding

- Rats that exhibit “high” responding in novel environment more readily self-administer drugs than “low” responders (Piazza et al).
- Do “high” responders also exhibit steeper delay discounting?

## High responders valued delayed rewards less

## Novelty Response and Delay Discounting in Two Inbred Mouse Strains: S129 vs C57

- Compared to C129, C57 mice:
- Respond more to novel environments
- Respond more (locomotor activity) to stimulants
- Self-administer alcohol more readily

## Novelty 

- Response

- C

- 5

- 7

- S

- 1

- 2

- 9

- 0

- 4

- 0

- 0

- 0

- 8

- 0

- 0

- 0

- 1

- 2

- 0

- 0

- 0

- *

- Distance Traveled

- S

- t

- r

- a

- i

- n

- K Value (higher k value =
- greater discounting)

- C

- 5

- 7

- S

- 1

- 2

- 9

- .2

- .4

- .6

- .8

- 1.0

- *

- S

- t

- r

- a

- i

- n

- K Value

## No Correlation Within Strains

- (I.e., strain differences related to genotype)

- 4

- 0

- 0

- 0

- 8

- 0

- 0

- 0

- 1

- 2

- 0

- 0

- 0

- 1

- 6

- 0

- 0

- 0

- 0

- .

- 0

- 0

- .

- 5

- 1

- .

- 0

- 1

- .

- 5

- 2

- .

- 0

- 2

- .

- 5

- C

- 5

- 7

- K Value

- D

- i

- s

- t

- a

- n

- c

- e

- T

- r

- a

- v

- e

- l

- e

- d

## Effects of Drugs on Delay Discounting (   = decrease in impulsivity )

## II. Behavioral InhibitionStop Task

- Ability to inhibit a prepotent response
- Subject told to respond as quickly as possible to a visual Go signal...
- but to _withhold_ the response if an auditory Stop signal is presented immediately after the Go signal
- How long does the individual need to Stop the response?

## Time

**Time**

**Time**

## Individual Differences in Stop RT on Stop Task

**Individual Differences in Stop RT on Stop Task**

- • ADHD children have slower Stop RT’s
- 	(Schachar et al, 1993)
- • Methylphenidate normalizes Stop RT in
- 	ADHD children (Tannock et al, 1989)
- • Cocaine users have slower Stop RT’s than
- 	controls (Fillmore and Rush, 2002)

## Healthy Volunteers: Distribution of 

**Healthy Volunteers: Distribution of **
**Stop Reaction Time** (N=165)

- 0

- 20

- 40

- 60

- 80

- 100

**Frequency**

- 50

- 100

- 150

- 200

- 250

- 300

- 350

- 400

- 450

- msec

## Healthy volunteers: Low positive correlations between Stop RT and personality (N=239)

- Correlations between Stop RT and Barratt Impulsivity Subscales
- Self-Control (r=.18, p=.005 ‘I [do not] plan tasks carefully’, ‘I am a careful thinker’, ‘I say things without thinking’)
- Attention (r=.19, p=.003) ‘I [do not] concentrate easily’, ‘I squirm at plays or lectures’, ‘I am [not] a steady thinker’)

## Is delay discounting (k value) related to behavioral inhibition (Stop RT)?

- • 165 healthy volunteers• correlation• factor analysis

## Delay Discounting (Log k value)

**100**

**200**

**300**

**400**

**500**

**600**

- -4

- -3

- -2

- -1

- 0

**Delay Discounting (Log k value)**

**Stop**
**RT**
- (msec)

**Stop RT and Delay Discounting not correlated**
- (N=165, r=.026, ns)

## Effects of drugs on Stop _x0008_RT

- Do drugs affect behavioral inhibition?
- Do drugs produce similar effects in humans and non-humans?
- Do drugs have similar effects on Stop RT and Delay Discounting?

## Effects of drugs on Stop RT(decrease in Stop RT = decrease in impulsivity)

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## Concordance between Delay Discounting and Stop Task in Rats

|  | Delay Discounting | Stop Task |
| --- | --- | --- |
| Alcohol | 
NO EFFECT |  |
| D-amphetamine |  |  |
| 5HT lesion | 
NO EFFECT |  |

## Conclusion 1: Delay Discounting procedures and the Stop Task are valid methods for measuring impulsive behavior

- 	• sensitive to individual differences
- 	• sensitive to drugs
- 	• good correspondence between humans and non-humans

## Conclusion 2:However, delay discounting and behavioral inhibition reflect separate processes

- 	• performance not correlated between individuals
- 	• factor analysis reveals separate processes
- 	• drugs have different effects

## Acknowledgments

- •  John Crean, PhD
- Justin Enggasser, MA
- Henry Chi, MA
- Jen McDonald, BA
- Andrea King, PhD
- Brady Reynolds,PhD
- Jim Zacny, PhD
- GCRC, NIDA