HEADREST FOR A MOTOR VEHICLE SEAT

The invention relates to a headrest (1) comprising a fixed part (2) and a movable part (3) connected to each other by means of an adjustment device (4) comprising: a tubular chamber (5) integral with said movable part - or respectively with said fixed part -; a piston integral with said fixed part - or respectively with said movable part -, said piston separating said chamber into two sub-chambers; a valve (9) arranged so as to allow communication between said sub-chambers to be cut off; an actuation means (10) of said valve in the opening direction; an incompressible fluid filling said chamber; so that said movable part can: be locked in relation to said fixed part when said valve is closed; be displaced in relation to said fixed part, by application of a force on said movable part, after actuation of said valve in the opening direction.