pioneering work of carl rovainen that began in the 1960s (see ), since the 1970s sten grillner and his colleagues at the karolinska institute in stockholm have used the lamprey as a model system to try to work out the principles of motor control in vertebrates, starting in the spinal cord and working upward into the brain. in common with other systems (see for a historical perspective of the idea), neural circuits within the spinal cord seem capable of generating some basic rhythmic motor patterns underlying swimming, and that these circuits are influenced by specific locomotor areas in the brainstem and midbrain, that are in turn influenced by higher brain structures including the basal ganglia and tectum. in a study of the lamprey tectum published in 2007, they found that electrical stimulation could elicit eye movements, lateral bending movements, or swimming activity, and that the type, amplitude, and direction of movement varied as a function of the location within the tectum that was stimulated. these findings were interpreted as consistent with the idea that the tectum generates goal-directed locomotion in the lamprey as shown in other species. birds drawing by ramon y cajal of several types of golgi-stained neurons in the optic tectum of a sparrow. in birds the optic tectum is involved in flight and is one of the largest brain components. the study of avian visual processing has enabled a greater understanding of that in mammals including humans.