R, for loop on data frame column and need value from an other

I have the following type of data frame:

   Gender FSIQ VIQ PIQ Weight Height MRIcount IQindicator
1  Female  133 132 124    118   64.5   816932           1
2    Male  140 150 124     NA   72.5  1001121           1
3    Male  139 123 150    143   73.3  1038437           1
4    Male  133 129 128    172   68.8   965353           1
5  Female  137 132 134    147   65.0   951545           1
6  Female   99  90 110    146   69.0   928799           0

My objective is to make 2 vectors, one with the MRIcount of which the IQindicator is 1 and the other for IQindicator is 0

I have written the following:

MRI_low <-c()
MRI_high <- c()
for (index in brain_data[,8]){
  if (index = 1){
    MRI_high <- append(MRI_high, MRIcount)
  } else {
    MRI_low <- append(MRI_low, MRIcount)
  }
}

How can I make this work?

for this example i would need:

> MRI_low <-c(928799) MRI_high <-c(816932, 1001121, 1038437, 965353,
> 951545)