Sentence:  Although we are still far from a complete understanding of these problems , as a <WSD>first</WSD> approximation , it is suggested that alterations in the hypothalamic balance with consequent changes in the hypothalamic cortical discharges account for major changes in behavior seen in various moods and states of emotions in man and beast under physiological circumstances , in experimental and clinical neurosis , and as the result of psychopharmacological agents . 
Meaning of the word marked with <WSD> tags:  preceding all others in time or space or degree