Interesting study.

However, I am wondering if 'hate' and 'love' could be pinned down as actual static measurable entities or elements to begin with. Your study seems to place emphasis on possibly pre-established understandings, namely that love and hate are to be points for take-off.

Could your study not indicate that 'hate' and 'love' are to be arrived at by means of pathways? In other words, it is not 'hate' or 'love' that could be measured but we could catch a glimpse within the human brain of which pathways are taken to arrive at either loving or hating someone, or something.

In that case, love and hate would be means, not ends onto themselves. The pathways open to hate and/or love will overlap to a certain extent because in either case the brain is trying to reach out for something. In the case of hate it cannot reach far enough whereas in the case of love it can be reached much further, hence possibly the deactivation within certain parts of the brain, setting in motion access to other necessary parts which in turn would be able to reach for better connections (in the case of love sans reason, perhaps?).

Your explanation: "What is not in doubt is that there is, in the behavioural sense, a strong link between the two sentiments and one can easily transmute into the other." would therefore turn out to be not a transmutation afterall, but would be a case of where one of the connections progresses (the love path) and the other (the path of hate) would be a cut-off, or stay put actively within the right superior frontal gyrus. Would it not be true that when love is replaced by hate that the 'other' (either someone or something) in relation to the self is no longer suficiently penetrable?

Some comments within the study seem presumptuous and may perhaps form an obstacle for heading in the right directions of understanding. When you mention for instance: "Hatred against an individual may be seemingly irrational and rooted in remote anthropological instincts. Hate based on race or religion would probably fall under this heading. On the other hand, an individual may trace the hatred to a past injustice and hence find a justifiable source for it." your study differentiates between the two. But it could be assumed that a hatred toward religion or race and a hatred toward injustice could all stem from the very same source, namely that either entity is 'mis-understood'and that such mis-understanding comes about by the self being unable to open necessary pathways. Religion, race and injustice all posses components within which are external to the self and need to be connected with. We do so by reason but we also find fruitfull connections by other means.

and

" We hypothesize that the sight of a hated person mobilizes the motor system for the possibility of attack or defense."

Perhaps the sight of a 'hated' person or entity mobilizes the motor system in particular ways because the self is no longer able to 'understand' the other and the motorization aspect of self will therefore be lead by frustration. Hate and love have as much to do with the self as they are related in connection to 'others'.

Just wondering.....