(From Dr. Susmit Kumar’s new book Karma, Mind, and Quest for Happiness iUniverse, 2012)
The brain is the center of the nervous system in all vertebrate, and most invertebrate, animals, including humans. For an example, humpback whales, great apes (like chimps and orangutans) and dolphins have "human" brain cells and they can think. Like humans, chimps and orangutans too plan for the future. Birds can distinguish our languages.  Human brain, weighing on average about three pounds, is an extremely complex structure that has evolved over millions of years. The difference between a human brain and the brains of other creatures is that the human brain has several capabilities that others do not have. Ours is the most advanced brain of all. According to David Linden, a professor of neuroscience at Johns Hopkins University: "Just as the mouse brain is a lizard brain with some extra stuff thrown on top, the human brain is essentially a mouse brain with extra toppings."This is one of the proofs that which establishes Darwin’s theory of evolution: Humans have evolved from animals.
Scientists have observed "brain-like" functions in plants also. Tiny strangleweed, a pale parasite plant, can sense the presence of friends, foes, and food and make adroit decisions on how to approach them. Unlike human beings, who may take aspirin as a fever suppressant, stressed plants produce an aspirin-like chemical that can be detected in the air above the plants. This chemical may be a kind of immune response that helps protect the plants. Studies have also shown the plants being eaten by animals also produce chemicals that can be sensed by other plants nearby. In addition to having an immune-like function, the chemical may be a means for plants to communicate to neighboring plants warning them of the threat.
A human brain has about 100 billion cells called neurons, each with up to 10,000 synapses. Synapses are junctions through which neurons signal to each other or form circuits with each other and to non-neuronal cells. In layman terms, a neuron has up to 10,000 wires coming out of it and hence it can connect to up to 10,000 other neurons or non-neuron cells. Hence our brain is an extremely complex structure. An adult brain can have hundreds of trillion connections. According to one study, the human brain is in some ways comparable to the interconnected network of the Internet.
A research team from the Humboldt University in Germany and the Erasmus Medical Center in the Netherlands found that the simulation of just one rat neuron could deliver the sensation of touch. They stimulated single neurons in rats and found this was enough to trigger a behavioral response when the rats’ whiskers were touched. Another US research suggests the computational ability of the brain cell could be even more complex, with different synapses - the many junctions between neurons and other nerve cells - able to act independently from those found elsewhere on the same cell. This could mean that, within a single neuron, different synapses could be storing (similar to our storing files on a computer’s hard drive) or processing completely different bits of information. Therefore it is beyond present imagination what our brain, with 100 billion neurons and each with up to 10,000 synapses, can do if harnessed efficiently.
All five sensory organs (vision, touch/skin, hearing, taste and smell) are constantly sending huge amount of information to the human brain. If you touch a hot or cold surface with a finger, your brain feels it immediately as each and every cell of your skin is constantly send data to the brain. For an example, the eye is forwarding 72 GB (Giga byte or 1,000,000,000 bytes) of data each second to the brain. Hence our brain may be getting trillions and trillions byte of data every second. Like a radio and television, which tune into a particular frequency, the human brain zeroes in on single bit of information out of the huge amount of data sent to it. Hence the human brain is very efficient.
As brain cells of animals like rats and monkeys are similar to humans, neuroscientists are conducting experiments on these animals to get new medicines and brain surgeries to treat human behaviors and diseases related to brain.
In the last couple of decades our knowledge about function and structure of the human brain and their effects on human behavior has improved a lot due to the technologies such as electro-encephalography (EEG), magneto-encephalography (MEG) and functional magnetic resonance imaging (fMRI). However, neurologists have just started to scratch the surface and they have a long way to go as the spatial resolutions of these techniques are very poor.
A day may come when science may be able to analyze the human brain with the help of the modern day computer, which may or may not turn out to yield correct results. A computer is defined on the basis of the speed of its processor (megahertz, gigahertz, etc.), hard drive size (in gigabyte) and memory size (in gigabyte). One "hertz" is one cycle per second - a computer with 1 gigahertz processor calculates 1,000,000,000 times per second, but then the type of chip of the processor also matters.
Today’s computers may or may not present the correct model of the human brain. Each human brain is unique in construction, i.e. the locations of hard drive and memory may not be at the same places in every human being. Apart from this it is proven clinically that the human brain generates new cells at any age.
One discovery surprised the neurosurgeons at the Toronto Western Hospital, Ontario. They were operating on a brain of a 190 kg obese man to control his appetite, inserting electrodes at the point in his brain controlling appetite and then stimulated it with an electric current. Instead of suppressing the appetite, it improved his memory. He recalled, in intricate detail, a scene from 30 years earlier. According to neurosurgeons, "He reported the experience of being in a park with friends from when he was around 20 years old and, as the intensity of stimulation increased, the details became more vivid. He recognized his girlfriend [at the time] ... The scene was in color. People were wearing identifiable clothes and were talking, but he could not decipher what they were saying," The hypothalamus has not usually been identified as a seat of memory. The contacts that most readily produced memories were located close to a structure called the fornix, an arched bundle of fibres that carries signals within the limbic system, which is involved in memory and emotions and is situated next to the hypothalamus. 
According to Professor Andres Lozano, "His performance improved dramatically. As we turned the current up, we first drove his memory circuits and improved his learning. As we increased the intensity of the current, we got spontaneous memories of discrete events. At a certain intensity, he would slash to the scene [in the park]. When the intensity was increased further, he got more detail but, when the current was turned off, it rapidly decayed. This is the first time that anyone has had electrodes implanted in the brain which have been shown to improve memory. We are driving the activity of the brain by increasing its sensitivity - turning up the volume of the memory circuits. Any event that involves the memory circuits is more likely to be stored and retained." Professor Lozano is a neurosurgeon at the Toronto Western Hospital, Ontario and a world authority on deep-brain stimulation who has undertaken 400 operations on Parkinson's disease sufferers.
This shows that there is a lot on our brain’s hard drive (i.e. brain cells where we store our past memories), but we can not get to some of these portions of our hard drive, i.e. we can not read from these brain cells.
 "Humpback whales have ‘human’ brain cells: study," Reuters, November 27, 2006; Linden, Eugene, "Can Animals Think?," Time, March 22, 1993.
 Lloyd, Robin, "Like Humans, Other Apes Plan Ahead," LiveScience.com, June 17, 2008.
 "Birds can distinguish languages: researchers," AFP, February 2, 2006.
 Begley, Sharon, "In our Messy, Reptilian Brains," Newsweek, April 9, 2007.
 Jonsson, Patrik, "New research opens a window on the minds of plants," abcnews.com, March 3, 2005.
 Schmid, Randolph E., "Stressed plants produce an aspirin-like chemical," AP, September 18, 2008.
 "Single brain cell’s power shown," BBC News, December 22, 2007.
 Laurance, Jeremy, "Scientists discover way to reverse loss of memory," The Independent (UK), January 30, 2008.