That may be a bit extreme, but according to results recently published in Neuron, we humans have an unexpectedly high degree of similarity with monkeys in the arrangement of the areas of our brain involved with language and thought processes. Fortunately, we humans have some differences as well. (Yes, even your big brother)
Researchers at the University of Oxford compared the ventrolateral frontal cortex regions of the brains of humans and macaque monkeys and found striking similarities in many areas. The ventrolateral frontal cortex is known to be an important area for language and other cognitive processes such as decision-making. The objective of the research is to better understand the connections in this area of the brain to potentially help treat neurological diseases or behavioral conditions that are strongly affected by this area.
MRI scans of the ventrolateral frontal cortex of 25 human subjects were compared by dividing the cortex into 12 separate regions of interest. The 12 different areas were consistent in their connections with the remaining areas of the brain, indicating that each area served unique functions.
MRI scans were then performed on the same number of macaque monkeys to compare the same sections of the ventrolateral frontal cortex. The research team was surprised to find that 11 of the 12 regions in the human brain had a corresponding area in the macaque brain, with significant similarity in the organization and connections between macaques and humans. The potential implication is that some human cognitive abilities may have their roots in these neural similarities.
However, one section of the human brain had no analogue in the macaque brain - an area known as the lateral frontal pole prefrontal cortex. This area of the human brain is known to have connections with decision-making and strategic planning skills, and is also associated with multi-tasking abilities.
Other differences were found in the macaque brains - with one of the more interesting differences relating to hearing. The connections between the ventrolateral frontal cortex and the areas of the brain that affect hearing are significantly different between humans and macaques. Monkeys do not perform well in auditory tasks, and this may be the reason why. It may also imply that humans use auditory input differently in our decisions and actions.
Some of the common areas of the human and macaque brains are the ones believed to be involved in ADHD, OCD and other compulsive psychiatric disorders. Therefore, it's possible that by studying the similar connections, scientists will be able to gain better insight into how specific brain connections relate to the presence of these disorders, and perhaps lead to new forms of treatment.
In the meantime, feel free to call your big brother and apologize to him - you really meant to call him 11/12ths of a monkey-brain.