Dear Erin,
Karl made another suggestion along the same lines as mine. You can add
single LGN source to your model (assuming you use ECD you can just put
it somewhere in the thalamus). This source will get the input. Then
you connect it to both left and right V1 with forward connections and
put left/right effect on those connections. You can actually specify
the effect as -1 1 and then see if you actually get opposite
directions of change for the two connections. Also note that if you
have LGN you should put your onset prior earlier than you would for V1
(50 msec?).
Best,
Vladimir
On Mon, Sep 12, 2011 at 8:46 PM, Vladimir Litvak
<[log in to unmask]> wrote:
> In fMRI things are different as 'conditions' and 'inputs' are closely
> related whereas in DCM-ERP they are different things. So I would
> rather ask whether the solution I suggested is equivalent to the case
> when you would have condition-specific inputs, which in theory can be
> implemented in DCM ERP. I think as long as you are not interested in
> intrinsic V1 connectivity, they should be. The only problem is that
> you expect the model to 'discover' the differences in the input
> whereas in the other case you could provide that information
> explicitly.
>
> Vladimir
>
> On Mon, Sep 12, 2011 at 8:36 PM, Mazerolle, Erin
> <[log in to unmask]> wrote:
>> Thanks for your reply Vladimir. That sounds reasonable to me. I have seen DCM fMRI papers (Stephan et al. 2005 for example) in which left visual field stimuli are driving inputs to right V1 and vice versa. Would you say that modelling conditional differences in intrinsic V1 connectivity results in an equivalent model?
>> Thanks again!
>> Erin
>>
>> ________________________________________
>> From: Vladimir Litvak [[log in to unmask]]
>> Sent: September 12, 2011 4:05 PM
>> To: Mazerolle, Erin
>> Cc: [log in to unmask]
>> Subject: Re: [SPM] DCM for ERP - driving inputs
>>
>> Dear Erin,
>>
>> You can have several different inputs by specifying several (not
>> necessarily different) values in the 'onset' box. However, these
>> inputs will be there for all conditions. One way around this is to
>> have one input for both V1s but allow the condition effect to modulate
>> the intrinsic V1 connectivity so that the responsiveness of V1 will be
>> much greater to contralateral than to ipsilateral stimulus. I'll ask
>> Karl if he thinks this an adequate solution for your situation and get
>> back to you if he suggests something different.
>>
>> Best,
>>
>> Vladimir
>>
>> On Mon, Sep 12, 2011 at 7:49 PM, Mazerolle, Erin
>> <[log in to unmask]> wrote:
>>> Hello,
>>>
>>> Is it possible to specify driving inputs for DCM for ERP such that different conditions drive different regions? I have only one column for the driving inputs (despite having multiple conditions defined). Are the events from all conditions modelled as driving inputs to the specified regions?
>>>
>>> I have a task in which stimuli were presented separately to the right and left visual fields, and would like to specify left visual field stimuli as driving input to right primary visual cortex, and right visual field stimuli as driving input to left primary visual cortex.
>>>
>>> Thank you in advance for your help,
>>> Erin
>>
>
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