(see fig. 2). They showed that this comprises two interwoven struc- 

 tures, both of which receive signals from the entire cerebral cortex, 

 the overall effect being reminiscent of a patchwork quilt. The two 

 components are now referred to as the matrix and the striosomes 

 (denoted by the letters m and s in the box labelled striatum in fig. 

 2). I believe that these two components are involved in overt and 

 covert muscular acts (the latter mediating thought), and that they 

 carry out their tasks individually when acts and thoughts run dif- 

 ferent courses. When we think about an act during its execution, 

 however, the matrix and striosome components must function in 

 unison. There is obvious scope for mutual influence between the 

 two streams of signals, if they are related to acts that are rather 

 similar. If I had recited Latin prose while the reader was tackling 

 the "gnu" sentence above, my words would have had no effect, but 

 if had switched to English, the reader might have had difficulty in 

 concentrating on the task. And if I had also spoken of gnus, the 

 reader might have become confused, and stopped altogether. Such 

 interference was originally studied by J. Ridley Stroop (1935), and 

 one can imagine it involving failure of mutual inhibition at the neu- 

 ronal level. 



Recalling that the basal ganglia (of which the striatum is a mem- 

 ber) are intimately involved in the control of drive, one could loose- 

 ly compare their role to that of an automobile clutch. And the par- 

 allel becomes a sad one when one notes that the underlying im- 

 pairment in Parkinson's disease has been traced to a faulty substantia 

 nigra (see substantia nigra Pars reticulata in fig. 2). The disease is 

 characterised by jerkiness when the patient attempts to initiate 

 movement, not unlike the jerky motion produced by the novice mo- 

 torist's failure to smoothly employ the clutch. Luder Deecke and his 

 colleagues (1977) have reported that the "readiness potential" dis- 

 cussed above (Kornhuber and Deecke, 1964) is much diminished in 

 Parkinson patients, and in some cases abolished altogether. 



When the basal ganglia are functioning as they should, they are 

 able to provide the drive that would, other factors permitting, lead 

 to overt action, or to thought, or to a combination of both. There 

 would then arise the question of how much harmony there is be- 

 tween the current drive and the current situation of the individual 



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